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/context_loader.py

@@ -1,3 +1,4 @@
+from datetime import datetime
 from pathlib import Path
 
 from persona import persona_path
@@ -36,6 +37,10 @@ def load_context(
     inara_dir = persona_path()
     parts = []
 
+    # ── 0. Current date and time (always — injected first so it's prominent) ──
+    now = datetime.now().astimezone()
+    parts.append(f"--- System ---\nCurrent date and time: {now.strftime('%A, %Y-%m-%d at %I:%M %p %Z')}")
+
     # ── 1. Core identity (always) ──────────────────────────────────
     for filename in _CORE:
         path = inara_dir / filename