fix(projects): watch session-project-map so Sessions tab refreshes

ProjectSessionsView's `.onChange(of: fileWatcher.lastChangeDate)`
was silently never firing when a new chat attributed a session to
a project — the sidecar was written correctly, the session was in
state.db correctly, attribution IDs matched exactly, but the per-
project Sessions list didn't auto-refresh.

Root cause: HermesFileWatcher.watchedCorePaths was missing
`paths.sessionProjectMap` (`~/.hermes/scarf/session_project_map.json`,
introduced in the v2.3 feature commit). Since the watcher didn't
observe that file, writes from SessionAttributionService.persist
produced no `lastChangeDate` change, the VM's onChange never ran,
and the Sessions tab stayed empty until the user navigated away
and back (triggering .task(id: project.id) to re-fire).

One-line fix: add the sidecar to the watched-paths array.

Now the flow works end-to-end:
1. User clicks "New Chat" on a project
2. ChatViewModel starts ACP session with cwd=project.path
3. SessionAttributionService.attribute writes the sidecar
4. HermesFileWatcher detects the change, bumps lastChangeDate
5. ProjectSessionsView's onChange fires, VM reloads, new session
   appears in the list immediately

80/80 tests still pass. No test change needed — the sidecar's
direct tests are in SessionAttributionServiceTests; this is a
file-watching integration fix.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scarf/scarf/Core/Services/HermesFileWatcher.swift

@@ -35,6 +35,16 @@ final class HermesFileWatcher {
             paths.errorsLog,
             paths.gatewayLog,
             paths.projectsRegistry,
+            // v2.3: sidecar attributing Hermes session IDs to Scarf project
+            // paths. Written by SessionAttributionService when a chat
+            // starts with a project context; read by
+            // ProjectSessionsViewModel to filter the session list. Without
+            // watching this file, the per-project Sessions tab would only
+            // pick up new sessions when the user re-entered the tab
+            // (triggering .task(id:) re-fire) — switching directly back
+            // to the project's Sessions tab after a chat left the tab
+            // stale.
+            paths.sessionProjectMap,
             paths.mcpTokensDir
         ]
     }