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>

.env.default

@@ -2,16 +2,27 @@
 # DO NOT commit .env — it contains secrets
 
 # ── Agent identity ───────────────────────────────────────────────────────────
-# Each running instance has its own identity directory and name.
-# For a second instance (e.g. Holly), copy this file, change these values,
-# set a different PORT and INARA_DIR, and run a separate systemd unit.
+# Global display names used in distillation prompts and session logs.
+# Individual persona identities live in home/{username}/persona/{name}/IDENTITY.md
 AGENT_NAME=Inara
 USER_NAME=Scott
 
+# ── Home directory ────────────────────────────────────────────────────────────
+# Root for all user/persona data. Layout: home/{username}/persona/{name}/
+# Relative paths are resolved from the cortex/ directory.
+# Default: ../home  (i.e. Cortex_and_Inara_dev/home/)
+# HOME_DIR=../home
+
 # ── Server ──────────────────────────────────────────────────────────────────
 HOST=0.0.0.0
 PORT=8000
 
+# ── Google Chat bot ──────────────────────────────────────────────────────────
+# JWT audience for verifying inbound Workspace Add-on Chat webhook requests.
+# For Workspace Add-on Chat apps, the aud claim = the endpoint URL.
+# Leave blank to disable verification (dev/testing only).
+GOOGLE_CHAT_AUDIENCE=https://cortex.dgrzone.com/channels/google-chat
+
 # ── Nextcloud Talk bot ───────────────────────────────────────────────────────
 NEXTCLOUD_URL=https://cloud.dgrzone.com
 NEXTCLOUD_TALK_BOT_SECRET=
@@ -27,7 +38,7 @@ TIMEOUT_GEMINI=120
 # ── Orchestrator (Gemini API — not Gemini CLI) ───────────────────────────────
 # Required for /orchestrate endpoint and tool use
 # Free tier key: https://aistudio.google.com/apikey
-GEMINI_API_KEY=AIzaSyAnmzm31zO1kFkphxCkTnwgFizbfgB1JHI
+GEMINI_API_KEY=
 
 # Model for the orchestration tool loop (not the user-facing response)
 ORCHESTRATOR_MODEL=gemini-2.5-flash