feat: match fleet to blueprint targets exactly

Add an optional exact blueprint mode with keep/create/remove previews, atomic queueing, cancellation of unstarted excess creations, and persistent dependencies for safe port reuse. Track removals alongside creations and preserve fill mode as the default.

Validation: type check, production build, and 103 deployment tests passed. The full suite has one telemetry assertion failure also reproduced on the previous commit.

Fixes #42

src/lib/server/db/schema.sql

@@ -467,7 +467,9 @@ CREATE TABLE IF NOT EXISTS server_launch_recipes (
 CREATE TABLE IF NOT EXISTS server_launch_collections (
     id TEXT PRIMARY KEY,
     name TEXT NOT NULL,
-    created_at TEXT NOT NULL
+    created_at TEXT NOT NULL,
+    mode TEXT NOT NULL DEFAULT 'fill',
+    retained_servers TEXT NOT NULL DEFAULT '[]'
 );
 
 CREATE TABLE IF NOT EXISTS server_collection_members (
@@ -483,9 +485,26 @@ CREATE TABLE IF NOT EXISTS server_collection_previews (
     blueprint_name TEXT NOT NULL,
     entries TEXT NOT NULL,
     servers TEXT NOT NULL,
+    mode TEXT NOT NULL DEFAULT 'fill',
+    fleet_snapshot TEXT,
     collection_id TEXT REFERENCES server_launch_collections(id) ON DELETE CASCADE
 );
 
+-- A pending removal can be shared by multiple reviewed collection requests.
+CREATE TABLE IF NOT EXISTS server_collection_removals (
+    collection_id TEXT NOT NULL REFERENCES server_launch_collections(id) ON DELETE CASCADE,
+    deployment_id TEXT NOT NULL REFERENCES server_deployments(id) ON DELETE CASCADE,
+    position INTEGER NOT NULL,
+    PRIMARY KEY (collection_id, deployment_id)
+);
+
+-- Reusing a port is safe only after the reviewed removal has completed.
+CREATE TABLE IF NOT EXISTS server_creation_dependencies (
+    deployment_id TEXT NOT NULL REFERENCES server_deployments(id) ON DELETE CASCADE,
+    removal_id TEXT NOT NULL REFERENCES server_deployments(id) ON DELETE CASCADE,
+    PRIMARY KEY (deployment_id, removal_id)
+);
+
 -- Persist state transitions atomically, including changes made by background workers.
 -- Polls with unchanged status/error do not produce duplicate activity entries.
 CREATE TABLE IF NOT EXISTS beta_events (