feat(agent): add manage_bg_jobs tool to inspect and kill background bash jobs (#4577)

Detached bash jobs (#!bg) could be launched and auto-reported on completion,
but the agent had no way to act on a running one: no on-demand output read and
no kill (it blocked until the 1h max-runtime). bg_jobs had the pieces
(_read_output, list_for_session, internal _kill) but none was exposed.

Adds:
- bg_jobs.kill(job_id): tears down the process tree, marks the job killed, and
  sets followed_up so the monitor does not also auto-continue a deliberate kill.
- manage_bg_jobs registry tool with actions list / output / kill, scoped to the
  chat that launched the job (cross-session access reads as not found).
- Wiring: TOOL_HANDLERS/TAGS, function schema, RAG index + keyword hints, parser
  name map, dispatch (threads session_id via _direct_fallback). Gated like bash
  (NON_ADMIN_BLOCKED_TOOLS; plan-mode mutator).
- agent_loop: background-job intent regex maps to the files domain (and the tool
  joins _DOMAIN_TOOL_MAP[files]) so short commands like 'kill that job' are not
  dropped by the low-signal gate that skips tool retrieval.
- bg launch message tells the model to call manage_bg_jobs itself for check/stop
  rather than printing raw tool syntax to the user.

Tests: tests/test_bg_job_tools.py (kill semantics, per-chat scoping, actions,
and the intent classifier).

src/tool_index.py

@@ -135,6 +135,7 @@ BUILTIN_TOOL_DESCRIPTIONS: Dict[str, str] = {
     "app_api": "Generic loopback to allowed Odysseus internal endpoints. Use this when the user wants something the UI can do but there's no named tool for it. Covers calendar, gallery, library/documents, memory, notes, tasks, settings, research, compare, cookbook GPUs/state — allowed UI buttons hit /api/* endpoints and you can hit them too. Sensitive auth/user/admin/shell paths and host-control Cookbook mutation routes are blocked; do NOT use app_api for shell commands, package installs, engine rebuilds, or PID signalling. Use named command tooling for shell commands. action='endpoints' with filter=<keyword> lists available endpoints. action='call' takes method+path+body. Hits same routes the UI uses — auth flows free. NOTE: themes are NOT an API endpoint — use the ui_control tool (create_theme / set_theme), not app_api. SESSIONS/CHATS: do NOT use app_api for these — GET /api/sessions returns EMPTY for tool calls (it's owner-filtered and tool calls authenticate as a different identity). EMAIL ACCOUNTS: do NOT use /api/email/accounts via app_api; use list_email_accounts, list_emails, and read_email instead. To list/rename/archive/delete/fork chats use the list_sessions and manage_session tools instead.",
     "edit_image": "Edit an image in the gallery: upscale (increase resolution), remove background (rembg), inpaint (fill selected area), or harmonize (blend edits). Specify image ID and action.",
     "trigger_research": "Start a deep research job on any topic — appears in the Deep Research sidebar, streams progress, produces a detailed report. Use for 'research X', 'look into Y', 'do deep research on Z', 'investigate'. NOT a scheduled task — it runs now and surfaces in the sidebar.",
+    "manage_bg_jobs": "Inspect and control detached background `bash` jobs (the ones started with a `#!bg` marker). action='list' shows this chat's jobs (id/status/age/command); action='output' returns a job's captured output so far (check on a long-running job, or re-read a finished one); action='kill' stops a runaway job by id. Use for 'is the background job done', 'check on that job', 'show the build output', 'kill the background job', 'stop the bg task'. output/kill need a job_id from list.",
 }
 
 
@@ -349,6 +350,12 @@ class ToolIndex:
             {"list_email_accounts", "list_emails", "read_email", "send_email", "reply_to_email", "bulk_email", "delete_email", "archive_email", "mark_email_read", "resolve_contact", "ui_control"},
         frozenset({"calendar", "event", "meeting", "schedule", "appointment"}):
             {"manage_calendar"},
+        # Detached background `bash` jobs (#!bg): check on / read output / kill.
+        frozenset({"background job", "background jobs", "bg job", "bg jobs",
+                   "background task", "is the job done", "check the job",
+                   "check on that job", "job output", "kill the job",
+                   "kill the background", "stop the background", "running job"}):
+            {"manage_bg_jobs"},
         frozenset({"note", "todo", "reminder", "remind", "checklist", "remember to"}):
             {"manage_notes"},
         # Chat/session management. "rename" alone maps to documents below, so a