feat: multi-user/multi-persona support with two-level home directory layout

Restructures persona storage from a flat personas/{name}/ layout to
home/{username}/persona/{name}/, mirroring Linux home directories.

Changes:
- persona.py: two ContextVars (user + persona), Linux-style name validation,
  set_context(), get_user(), get_persona(), validate(), list_users(),
  list_user_personas(); persona_path() takes (username, name)
- config.py: replaces personas_dir with home_dir + home_root()
- git mv personas/inara → home/scott/persona/inara (history preserved)
- home/holly/persona/tina/: Holly's persona stub added
- cron_runner.py: all storage functions take (username, persona) params
- tools/cron.py: stamps user + persona on jobs; APScheduler IDs are
  {user}:{persona}:{job_id} to prevent collisions across users
- memory_distiller.py: distill_short/mid/long take (username, persona);
  added missing Path + settings imports
- scheduler.py: _load_user_crons() iterates home/*/persona/* (two-level)
- routers/chat.py, orchestrator.py: user field added; set_context() called
- tests/conftest.py: home_root fixture with two-level structure;
  patches home_dir instead of personas_dir
- tests/test_persona.py: fully rewritten for two-level API
- tests/test_api_files.py: updated fixture name and path
- .env.default: documents HOME_DIR setting; scrubs stale API key
- CLAUDE.md, README.md: directory maps updated for new layout

All 80 tests pass.

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

home/scott/persona/inara/README.md

@@ -0,0 +1,32 @@
+# Inara — Identity & Memory Layer
+
+This directory is Inara's home. It contains everything needed to instantiate her as a
+consistent, persistent agent across any model or runtime.
+
+## Files
+
+| File | Tier | Purpose |
+|------|------|---------|
+| `SOUL.md` | Always | Core identity, traits, how she behaves |
+| `IDENTITY.md` | Always | Name, vibe, emoji — the short card |
+| `USER.md` | T1+ | Scott's profile — who she's helping |
+| `MEMORY.md` | T2+ | Curated long-term memory (keep under 4k tokens) |
+| `PROTOCOLS.md` | T2+ | Fleet rules, safety, delegation, memory management |
+| `CONTEXT_TIERS.md` | Dispatcher | Which files to load per model context size |
+| `sessions/` | T3+ | Daily session logs (raw), format: `YYYY-MM-DD.md` |
+
+## Loading Order
+
+Always load in this order to establish context before adding detail:
+1. `SOUL.md`
+2. `IDENTITY.md`
+3. `USER.md`
+4. `MEMORY.md`
+5. `PROTOCOLS.md`
+6. Session files (most recent first)
+
+See `CONTEXT_TIERS.md` for the full dispatcher spec.
+
+## Secrets
+
+Credentials, API keys, and tokens live in `.env` only — never in these files.