feat: per-role inject_mode, OTR fixes, hover metadata, send/stop tooltip

- inject_mode: per-role toggle (parallel to inject_datetime) gates the
  "Current mode: Off The Record" line in the system prompt; wired through
  model_registry, context_loader, chat router, orchestrator router, and
  local_llm settings UI

- OTR orchestrator fix: OrchestrateRequest now carries off_record;
  _finalize_job stores it per message and gates log_turn on it; JS
  orchestrate payload sends off_record correctly

- Per-message hover metadata: removed always-visible .model-tag; replaced
  with .msg-meta strip in the action bar (hover-only); shows model label,
  host, fallback indicator, and OTR badge; stored in session JSON

- Send/stop button tooltip: shows role + model and (when tools on)
  separate orchestrator model + engine label; live elapsed timer on stop
  button via startRunTimer/stopRunTimer

- OrchestratorResult.backend_label: new field; openai_orchestrator fills
  it; finalize_job propagates it to job dict and session messages

- GET /backend: exposes orchestrator_model label so the frontend tooltip
  can show both models separately

- TODO: session delete confirmation added

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

documentation/TODO__Agents.md

@@ -116,6 +116,13 @@ Inara reaches out on her own initiative via NC Talk, Google Chat, email, or brow
 - [x] `POST /api/push/test` + `POST /api/push/reminders/check` — on-demand test endpoints
 - [x] `push_utils.py` — fixed `pywebpush` 2.x key deserialisation (use `Vapid.from_pem()` instead of passing PEM string)
 
+### [UX] Session delete confirmation
+The session delete button in the sidebar needs a confirmation step before firing — currently
+it deletes immediately on click with no undo. A simple `confirm()` dialog or an inline
+"Are you sure? [Delete] [Cancel]" reveal would prevent accidental data loss.
+- [ ] Add confirm step to session delete button click handler in `app.js`
+- [ ] Consider: also confirm for message-level delete (Edit/Delete hover controls)
+
 ### [UI] File attachments in chat
 Upload an image or document inline and have it flow into context. Natural workflow
 ("here's this PDF, summarize it"); local backend already supports multimodal via Open WebUI.