feat: proper confirmation-resume flow + per-user tool policy

Fixes the broken confirmation gate where users had no way to approve
or deny a blocked tool call in the web UI.

Changes:
- orchestrator_engine.py: add OrchestrateCheckpoint dataclass, extract
  loop into _run_from_contents(), add resume() function
- openai_orchestrator.py: same treatment — _run_from_messages(), resume()
- routers/orchestrator.py: POST /{job_id}/confirm and /deny endpoints,
  separate _checkpoints store, _resume_job() + _finalize_job() helpers,
  "awaiting_confirmation" job status with pending_confirmation payload
- auth_utils.py: get_tool_policy() and save_tool_policy() helpers reading
  home/{user}/tool_policy.json (allow/deny lists)
- routers/orchestrator.py: loads tool_policy per user and passes
  confirm_allow/confirm_deny to both engines
- app.js: poll loop handles awaiting_confirmation — shows Confirm/Deny
  buttons inline, resumes polling after user action
- settings.html + settings.py: Tool Permissions section with allow/deny
  textareas, POST /settings/tool-policy route
- style.css: .confirm-gate, .confirm-btn, .deny-btn styles

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

cortex/static/style.css

@@ -546,6 +546,25 @@
 
         .message.thinking { color: var(--muted); font-style: italic; }
 
+        /* Confirmation gate */
+        .confirm-gate { display: flex; flex-direction: column; gap: 0.6rem; }
+        .confirm-gate p { margin: 0; }
+        .confirm-tools { font-size: 0.82rem; color: var(--muted); }
+        .confirm-actions { display: flex; gap: 0.5rem; margin-top: 0.25rem; }
+        .confirm-btn, .deny-btn {
+            padding: 0.35rem 0.9rem;
+            border-radius: 6px;
+            border: none;
+            font-size: 0.85rem;
+            font-weight: 600;
+            cursor: pointer;
+            transition: opacity 0.15s;
+        }
+        .confirm-btn { background: #16a34a; color: #fff; }
+        .confirm-btn:hover { opacity: 0.85; }
+        .deny-btn { background: var(--surface); border: 1px solid var(--border); color: var(--text); }
+        .deny-btn:hover { border-color: var(--muted); }
+
         /* Copy button */
         .message.assistant, .message.user { position: relative; }