Initial implementation: host lifecycle + PXE + admin dashboard

Go service for Proxmox homelab cluster provisioning. Handles PXE boot,
Proxmox autoinstall (answer file generation), cluster join via SSH,
and Infrastructure API registration.

- Host state machine (registered → pxe_ready → installing → ready)
- dnsmasq supervisor with MAC-based allowlist
- iPXE script and Proxmox answer file generation
- First-boot phone-home → cluster join → infra registration
- Operation locking with expiry (409 on conflict)
- SSE event hub for real-time dashboard updates
- Admin dashboard (host grid, detail, registration form)
- Config-driven server types with hot-reload
- Docker deployment (multi-stage fat image)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/db/migrations/0001_init.sql

@@ -0,0 +1,43 @@
+CREATE TABLE hosts (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    hostname      TEXT NOT NULL UNIQUE,
+    mac           TEXT NOT NULL UNIQUE,
+    server_type   TEXT NOT NULL,
+    state         TEXT NOT NULL DEFAULT 'registered',
+    ip_address    TEXT,
+    hardware_id   TEXT,
+    infra_host_id INTEGER,
+    notes         TEXT NOT NULL DEFAULT '',
+    created_at    TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ','now')),
+    updated_at    TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ','now'))
+);
+
+CREATE TABLE operations (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    host_id       INTEGER NOT NULL REFERENCES hosts(id) ON DELETE CASCADE,
+    kind          TEXT NOT NULL,
+    state         TEXT NOT NULL DEFAULT 'active',
+    image_id      INTEGER REFERENCES images(id),
+    started_at    TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ','now')),
+    completed_at  TEXT,
+    error_message TEXT
+);
+CREATE INDEX idx_operations_host ON operations(host_id);
+
+CREATE TABLE operation_locks (
+    host_id       INTEGER PRIMARY KEY REFERENCES hosts(id) ON DELETE CASCADE,
+    operation_id  INTEGER NOT NULL REFERENCES operations(id),
+    locked_at     TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ','now')),
+    expires_at    TEXT NOT NULL
+);
+
+CREATE TABLE images (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    name          TEXT NOT NULL UNIQUE,
+    kind          TEXT NOT NULL,
+    version       TEXT NOT NULL,
+    kernel_path   TEXT NOT NULL,
+    initrd_path   TEXT NOT NULL,
+    is_default    INTEGER NOT NULL DEFAULT 0,
+    created_at    TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ','now'))
+);