feat: rework EOL, repairs, and hosts for real workflow

Four domain-model changes driven by exercising the deployed 2.0 build:

- EOL moves from manufacturer to MPN via new PartModel catalog table,
  so alerts fire on the thing that actually ages.
- Repairs re-home to Host (required hostId + problem text) with an
  optional RepairJobPart join for affected parts; drop Part.replacementPartId.
- New /repairs/:id detail page with editable problem, part list, and
  a RepairComment thread (REPAIR_COMMENTED events fan out to each
  problem part's timeline).
- Host.assetId (required, unique) surfaces prominently on the repair
  page so techs can confirm they're touching the right box.

Single destructive migration reshapes existing dev data. All 7 packages
typecheck clean; 30 API tests pass (9 new covering host membership,
upsertByMpn idempotency + race, assetId 409, comment userId stamping).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/db/prisma/schema.prisma

@@ -16,16 +16,17 @@ datasource db {
 }
 
 model User {
-  id                String         @id @default(uuid())
-  username          String         @unique
-  email             String         @unique
+  id                String          @id @default(uuid())
+  username          String          @unique
+  email             String          @unique
   passwordHash      String
-  role              String         @default("TECHNICIAN")
-  createdAt         DateTime       @default(now())
-  updatedAt         DateTime       @updatedAt
+  role              String          @default("TECHNICIAN")
+  createdAt         DateTime        @default(now())
+  updatedAt         DateTime        @updatedAt
   partEvents        PartEvent[]
   refreshTokens     RefreshToken[]
-  repairAssignments RepairJob[]    @relation("RepairAssignee")
+  repairAssignments RepairJob[]     @relation("RepairAssignee")
+  repairComments    RepairComment[]
   savedViews        SavedView[]
   csvImportJobs     CsvImportJob[]
 }
@@ -45,12 +46,28 @@ model RefreshToken {
 }
 
 model Manufacturer {
-  id        String    @id @default(uuid())
-  name      String    @unique
-  eolDate   DateTime?
-  createdAt DateTime  @default(now())
-  updatedAt DateTime  @updatedAt
-  parts     Part[]
+  id         String      @id @default(uuid())
+  name       String      @unique
+  createdAt  DateTime    @default(now())
+  updatedAt  DateTime    @updatedAt
+  parts      Part[]
+  partModels PartModel[]
+}
+
+model PartModel {
+  id             String       @id @default(uuid())
+  manufacturerId String
+  manufacturer   Manufacturer @relation(fields: [manufacturerId], references: [id], onDelete: Restrict)
+  mpn            String
+  eolDate        DateTime?
+  notes          String?
+  createdAt      DateTime     @default(now())
+  updatedAt      DateTime     @updatedAt
+  parts          Part[]
+
+  @@unique([manufacturerId, mpn])
+  @@index([manufacturerId])
+  @@index([eolDate])
 }
 
 model Site {
@@ -97,33 +114,33 @@ model Category {
 }
 
 model Part {
-  id                String       @id @default(uuid())
-  serialNumber      String       @unique
-  mpn               String
-  manufacturerId    String
-  manufacturer      Manufacturer @relation(fields: [manufacturerId], references: [id], onDelete: Restrict)
-  price             Float?
-  state             String       @default("SPARE")
-  binId             String?
-  bin               Bin?         @relation(fields: [binId], references: [id], onDelete: SetNull)
-  categoryId        String?
-  category          Category?    @relation(fields: [categoryId], references: [id], onDelete: SetNull)
-  replacementPartId String?
-  replacement       Part?        @relation("PartReplacement", fields: [replacementPartId], references: [id], onDelete: SetNull)
-  replacedBy        Part[]       @relation("PartReplacement")
-  notes             String?
-  createdAt         DateTime     @default(now())
-  updatedAt         DateTime     @updatedAt
-  events            PartEvent[]
-  tags              PartTag[]
-  repairs           RepairJob[]
+  id             String          @id @default(uuid())
+  serialNumber   String          @unique
+  partModelId    String
+  partModel      PartModel       @relation(fields: [partModelId], references: [id], onDelete: Restrict)
+  manufacturerId String
+  manufacturer   Manufacturer    @relation(fields: [manufacturerId], references: [id], onDelete: Restrict)
+  price          Float?
+  state          String          @default("SPARE")
+  binId          String?
+  bin            Bin?            @relation(fields: [binId], references: [id], onDelete: SetNull)
+  categoryId     String?
+  category       Category?       @relation(fields: [categoryId], references: [id], onDelete: SetNull)
+  hostId         String?
+  host           Host?           @relation(fields: [hostId], references: [id], onDelete: SetNull)
+  notes          String?
+  createdAt      DateTime        @default(now())
+  updatedAt      DateTime        @updatedAt
+  events         PartEvent[]
+  tags           PartTag[]
+  problemInRepairs RepairJobPart[]
 
   @@index([state])
   @@index([binId])
   @@index([manufacturerId])
-  @@index([mpn])
+  @@index([partModelId])
   @@index([categoryId])
-  @@index([replacementPartId])
+  @@index([hostId])
 }
 
 model PartEvent {
@@ -164,36 +181,61 @@ model PartTag {
 
 model Host {
   id        String      @id @default(uuid())
+  assetId   String      @unique
   name      String      @unique
   location  String?
   notes     String?
   createdAt DateTime    @default(now())
   updatedAt DateTime    @updatedAt
+  parts     Part[]
   repairs   RepairJob[]
 }
 
 model RepairJob {
-  id         String    @id @default(uuid())
-  partId     String
-  part       Part      @relation(fields: [partId], references: [id], onDelete: Cascade)
-  hostId     String?
-  host       Host?     @relation(fields: [hostId], references: [id], onDelete: SetNull)
-  assigneeId String?
-  assignee   User?     @relation("RepairAssignee", fields: [assigneeId], references: [id], onDelete: SetNull)
-  status     String    @default("PENDING")
-  openedAt   DateTime  @default(now())
-  closedAt   DateTime?
-  notes      String?
-  createdAt  DateTime  @default(now())
-  updatedAt  DateTime  @updatedAt
+  id           String          @id @default(uuid())
+  hostId       String
+  host         Host            @relation(fields: [hostId], references: [id], onDelete: Restrict)
+  assigneeId   String?
+  assignee     User?           @relation("RepairAssignee", fields: [assigneeId], references: [id], onDelete: SetNull)
+  status       String          @default("PENDING")
+  problem      String
+  openedAt     DateTime        @default(now())
+  closedAt     DateTime?
+  notes        String?
+  createdAt    DateTime        @default(now())
+  updatedAt    DateTime        @updatedAt
+  problemParts RepairJobPart[]
+  comments     RepairComment[]
 
-  @@index([partId])
   @@index([status])
   @@index([hostId])
   @@index([assigneeId])
   @@index([status, openedAt(sort: Desc)])
 }
 
+model RepairJobPart {
+  repairJobId String
+  partId      String
+  repairJob   RepairJob @relation(fields: [repairJobId], references: [id], onDelete: Cascade)
+  part        Part      @relation(fields: [partId], references: [id], onDelete: Restrict)
+  createdAt   DateTime  @default(now())
+
+  @@id([repairJobId, partId])
+  @@index([partId])
+}
+
+model RepairComment {
+  id          String    @id @default(uuid())
+  repairJobId String
+  repairJob   RepairJob @relation(fields: [repairJobId], references: [id], onDelete: Cascade)
+  userId      String?
+  user        User?     @relation(fields: [userId], references: [id], onDelete: SetNull)
+  content     String
+  createdAt   DateTime  @default(now())
+
+  @@index([repairJobId, createdAt])
+}
+
 model WebhookSubscription {
   id        String   @id @default(uuid())
   url       String