feat: audit log, usage tracking UI, OpenAI orchestrator compaction, onboarding + docs

Tool audit log:
- Every orchestrator tool call logged to home/{user}/tool_audit/YYYY-MM-DD.jsonl
- Files panel sidebar: audit log group (collapsed), date-linked read-only table
- Admin endpoints: /api/audit/files, /api/audit/day, /api/audit/recent, /api/audit/stats
- Engine and model name recorded per entry

OpenAI orchestrator improvements:
- Context budget enforcement: 75% of model context_k (min 16k)
- Message compaction: truncates old tool results when approaching budget
- max_rounds respected per model config (intersected with server cap)

OpenRouter onboarding (setup.html, onboarding.py, app.js, settings.html):
- Step 3 of 3: /setup/model with curated model picker
- Chat banner for users on server-default model (informational, not alarmist)
- Settings quick-link card; /setup/model works standalone for existing users

Model registry + session store:
- set_role_config / get_role_config for per-role tool lists and system_append
- session_store: session rename, session name backfill endpoint

UI updates (app.js, index.html, style.css, local_llm.html):
- Role toggle in context panel
- Off-the-record mode
- Agent notes read-only viewer
- OPERATIONS.md loaded at T2+ in context

Documentation:
- HELP.md: full tool table, per-role tool sets, Agent Notes, usage tracking
- TOOLS.md: Agent Notes section, count corrected to 44
- ARCH__SYSTEM.md, ARCH__BACKENDS.md, MASTER.md updated to match reality
- CLAUDE.md: onboarding flow, documentation philosophy sections
- README.md: stack in practice, DeepSeek TUI mention, architecture diagram updated
- TODO__Agents.md: onboarding task completed with deviation notes

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

cortex/session_store.py

@@ -112,16 +112,17 @@ def list_all() -> list[dict]:
     if not d.exists():
         return []
     results = []
-    for f in sorted(d.glob("*.json"), key=lambda p: p.stat().st_mtime, reverse=True):
+    for f in d.glob("*.json"):
         try:
             data = json.loads(f.read_text())
-            entry = {
+            results.append({
                 "session_id": data["session_id"],
                 "name": data.get("name", ""),
                 "updated": data.get("updated"),
                 "message_count": len(data.get("messages", [])),
-            }
-            results.append(entry)
+                "_sort_key": data.get("updated") or f.stat().st_mtime,
+            })
         except Exception:
             pass
+    results.sort(key=lambda s: s.pop("_sort_key"), reverse=True)
     return results