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/routers/files.py

@@ -27,10 +27,21 @@ ALLOWED = {
     "MEMORY_SHORT.bak1.md",
     "MEMORY_SHORT.bak2.md",
     "HELP.md",
+    # Agent private notes — backups only; AGENT_NOTES.md itself is agent-only
+    "AGENT_NOTES.bak1.md",
+    "AGENT_NOTES.bak2.md",
+    "AGENT_NOTES.bak3.md",
+}
+
+# Files that can be read via the panel but not written by users
+READ_ONLY = {
+    "AGENT_NOTES.bak1.md",
+    "AGENT_NOTES.bak2.md",
+    "AGENT_NOTES.bak3.md",
 }
 
 # Files served from home/{user}/ instead of persona path
-USER_FILES = {"email_allowlist.json"}
+USER_FILES = {"email_allowlist.json", "usage.json"}
 
 
 def _resolve(user: str, persona: str) -> None:
@@ -92,7 +103,11 @@ async def get_file(
     p = _path(filename, user=user)
     if not p.exists():
         raise HTTPException(status_code=404, detail=f"{filename} does not exist")
-    return {"name": filename, "content": p.read_text()}
+    return {
+        "name": filename,
+        "content": p.read_text(),
+        "readonly": filename in READ_ONLY,
+    }
 
 
 class FileWrite(BaseModel):
@@ -106,6 +121,8 @@ async def save_file(
     user: str = Query("scott"),
     persona: str = Query("inara"),
 ) -> dict:
+    if filename in READ_ONLY:
+        raise HTTPException(status_code=403, detail=f"{filename} is read-only.")
     _resolve(user, persona)
     p = _path(filename, user=user)
     p.write_text(req.content)