feat: M6 maintenance windows + M7 WebSocket relay (real-time job status)

M6 - Maintenance Windows:
- routes/maintenance_windows.rs: full CRUD API
- migrations/004_maintenance_windows.sql
- frontend/MaintenanceWindowsPage.tsx
- HostDetailPage.tsx: maintenance window config panel

M7 - WebSocket Relay:
- pm-web: POST /api/v1/ws/ticket (JWT-auth, single-use, 60s TTL)
- pm-web: WS /api/v1/ws/jobs?ticket=... (PgListener -> browser push)
- pm-web: DashMap<String,WsTicket> in AppState, 30s cleanup task
- pm-worker: ws_relay.rs subscribes to agent WS, updates patch_job_hosts,
  fires pg_notify(job_update) for real-time fan-out
- frontend: useJobWebSocket hook with auto-reconnect + exponential backoff
- frontend: JobsPage live updates with WS status indicator
- types: JobWsEvent interface
- api/client: wsApi.createTicket()

All tasks marked complete in tasks/todo.md
cargo build: zero errors, zero warnings

Cargo.lock

@@ -134,7 +134,7 @@ dependencies = [
  "sha1",
  "sync_wrapper",
  "tokio",
- "tokio-tungstenite",
+ "tokio-tungstenite 0.29.0",
  "tower",
  "tower-layer",
  "tower-service",
@@ -455,6 +455,20 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "dashmap"
+version = "6.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5041cc499144891f3790297212f32a74fb938e5136a14943f338ef9e0ae276cf"
+dependencies = [
+ "cfg-if",
+ "crossbeam-utils",
+ "hashbrown 0.14.5",
+ "lock_api",
+ "once_cell",
+ "parking_lot_core",
+]
+
 [[package]]
 name = "data-encoding"
 version = "2.10.0"
@@ -1807,6 +1821,7 @@ dependencies = [
  "axum",
  "axum-extra",
  "chrono",
+ "dashmap",
  "ipnet",
  "pm-auth",
  "pm-core",
@@ -1832,11 +1847,15 @@ dependencies = [
  "futures",
  "pm-agent-client",
  "pm-core",
+ "rustls",
+ "rustls-pemfile",
  "serde",
  "serde_json",
  "sqlx",
  "thiserror",
  "tokio",
+ "tokio-rustls",
+ "tokio-tungstenite 0.26.2",
  "tracing",
  "tracing-subscriber",
  "uuid",
@@ -2192,6 +2211,15 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "rustls-pemfile"
+version = "2.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dce314e5fee3f39953d46bb63bb8a46d40c2f8fb7cc5a3b6cab2bde9721d6e50"
+dependencies = [
+ "rustls-pki-types",
+]
+
 [[package]]
 name = "rustls-pki-types"
 version = "1.14.0"
@@ -2918,6 +2946,22 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "tokio-tungstenite"
+version = "0.26.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a9daff607c6d2bf6c16fd681ccb7eecc83e4e2cdc1ca067ffaadfca5de7f084"
+dependencies = [
+ "futures-util",
+ "log",
+ "rustls",
+ "rustls-pki-types",
+ "tokio",
+ "tokio-rustls",
+ "tungstenite 0.26.2",
+ "webpki-roots 0.26.11",
+]
+
 [[package]]
 name = "tokio-tungstenite"
 version = "0.29.0"
@@ -2927,7 +2971,7 @@ dependencies = [
  "futures-util",
  "log",
  "tokio",
- "tungstenite",
+ "tungstenite 0.29.0",
 ]
 
 [[package]]
@@ -3169,6 +3213,25 @@ version = "0.2.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e421abadd41a4225275504ea4d6566923418b7f05506fbc9c0fe86ba7396114b"
 
+[[package]]
+name = "tungstenite"
+version = "0.26.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4793cb5e56680ecbb1d843515b23b6de9a75eb04b66643e256a396d43be33c13"
+dependencies = [
+ "bytes",
+ "data-encoding",
+ "http",
+ "httparse",
+ "log",
+ "rand 0.9.4",
+ "rustls",
+ "rustls-pki-types",
+ "sha1",
+ "thiserror",
+ "utf-8",
+]
+
 [[package]]
 name = "tungstenite"
 version = "0.29.0"
@@ -3283,6 +3346,12 @@ version = "2.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "daf8dba3b7eb870caf1ddeed7bc9d2a049f3cfdfae7cb521b087cc33ae4c49da"
 
+[[package]]
+name = "utf-8"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09cc8ee72d2a9becf2f2febe0205bbed8fc6615b7cb429ad062dc7b7ddd036a9"
+
 [[package]]
 name = "utf8_iter"
 version = "1.0.4"