feat: multi-persona support (single Cortex, multiple users)

- Add cortex/persona.py: ContextVar-based per-request routing with
  path traversal protection and persona validation
- Migrate inara/ → personas/inara/ (git history preserved via git mv)
- config.py: add personas_root(), inara_path() delegates to personas/inara
- All 14 settings.inara_path() call sites replaced with persona_path()
- ChatRequest + OrchestrateRequest: add persona field (default: "inara")
  with validation at request entry before any processing
- memory_distiller: add optional persona param for future per-persona distill
- cron_runner/tools/cron: stamp persona on jobs, prefix APScheduler IDs
  (persona:job_id) to prevent collisions across personas
- scheduler: _load_user_crons() iterates all personas at startup

Adding a new persona: create personas/<name>/ with IDENTITY.md + SOUL.md.
Auth: handled at nginx level (inject X-Cortex-Persona header per subdomain).
Future: persona maps to Aether account_id_random for full integration.

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

cortex/routers/chat.py

@@ -8,6 +8,7 @@ from llm_client import complete
 from session_logger import log_turn
 from session_store import load as load_session, save as save_session, list_all, generate_session_id, delete as delete_session
 from config import settings
+from persona import set_persona, validate as validate_persona
 import event_bus
 
 
@@ -22,6 +23,7 @@ class ChatRequest(BaseModel):
     include_long: bool = True
     include_mid: bool = True
     include_short: bool = True
+    persona: str = "inara"
 
 
 class BackendRequest(BaseModel):
@@ -49,6 +51,12 @@ async def _stream_chat(req: ChatRequest):
               "backend": "...", "fallback_used": bool}
       data: {"type": "error", "message": "..."}
     """
+    try:
+        set_persona(validate_persona(req.persona))
+    except ValueError as e:
+        yield f"data: {json.dumps({'type': 'error', 'message': str(e)})}\n\n"
+        return
+
     session_id = req.session_id or generate_session_id()
     tier = req.tier or settings.default_tier