fix: multi-user distillation + datetime in context + session log labels

Distillation was silently operating on scott/inara for all users due to
ContextVar defaults. All three distill endpoints now require ?user=&persona=
query params and validate them via persona.validate(). Memory distiller
signatures changed from Optional to required positional args — no more
global settings fallback. Scheduler now iterates all users/personas instead
of hardcoding the primary user.

- context_loader: inject current date/time as first system prompt section
- session_logger: use get_user()/get_persona() from context instead of
  settings globals so Holly/Brian sessions show correct speaker labels
- memory_distiller: system prompts now reference u.title()/p.title()
  instead of settings.user_name/settings.agent_name
- distill router: Query(...) enforces params; _resolve() validates persona
- scheduler: _all_personas() helper iterates every user/persona for distill
- app.js: runDistill() now appends ?user=&persona= via _fileParams

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

cortex/session_logger.py

@@ -1,6 +1,5 @@
 from datetime import datetime
-from config import settings
-from persona import persona_path
+from persona import persona_path, get_user, get_persona
 
 
 def log_turn(
@@ -21,11 +20,15 @@ def log_turn(
     meta_parts = [p for p in [backend_label, host] if p]
     meta = f" · {' / '.join(meta_parts)}" if meta_parts else ""
 
+    # Use the actual user/persona names from the current request context
+    user_label = get_user().title()
+    persona_label = get_persona().title()
+
     with open(log_file, "a") as f:
         if is_new:
             f.write(f"# Session Log — {today}\n")
         f.write(
             f"\n### [{timestamp}] `{session_id}`{meta}\n"
-            f"**{settings.user_name}:** {user_msg}\n\n"
-            f"**{settings.agent_name}:** {assistant_msg}\n"
+            f"**{user_label}:** {user_msg}\n\n"
+            f"**{persona_label}:** {assistant_msg}\n"
         )