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>

cortex/tests/conftest.py

@@ -2,10 +2,19 @@
 Shared fixtures for Cortex test suite.
 
 Key design choices:
-  - All file I/O goes to a tmp_path, never touching personas/inara/ or real sessions.
+  - All file I/O goes to a tmp_path, never touching home/ or real sessions.
   - LLM calls are mocked by default — tests are fast and deterministic.
-  - The 'app' fixture patches settings before importing main, so all modules
+  - The 'client' fixture patches settings before importing main, so all modules
     see the temp directory.
+
+Home layout mirrors the two-level structure:
+  tmp/
+    scott/
+      persona/
+        inara/    ← the default test persona
+    holly/
+      persona/
+        tina/
 """
 
 import json
@@ -19,19 +28,21 @@ from httpx import ASGITransport
 
 
 # ---------------------------------------------------------------------------
-# Temp persona directory
+# Temp home directory
 # ---------------------------------------------------------------------------
 
 @pytest.fixture(scope="session")
-def personas_root(tmp_path_factory) -> Path:
-    """A temp personas/ dir with a minimal 'inara' persona for testing."""
-    root = tmp_path_factory.mktemp("personas")
-    _make_persona(root, "inara", "Inara", "Scott")
+def home_root(tmp_path_factory) -> Path:
+    """A temp home/ dir with minimal user/persona stubs for testing."""
+    root = tmp_path_factory.mktemp("home")
+    _make_persona(root, "scott", "inara", "Inara", "Scott")
+    _make_persona(root, "holly", "tina",  "Tina",  "Holly")
     return root
 
 
-def _make_persona(root: Path, name: str, agent: str, user: str) -> Path:
-    p = root / name
+def _make_persona(root: Path, username: str, persona: str,
+                  agent: str, user: str) -> Path:
+    p = root / username / "persona" / persona
     p.mkdir(parents=True, exist_ok=True)
     (p / "IDENTITY.md").write_text(f"# {agent}\nTest identity for {agent}.")
     (p / "SOUL.md").write_text(f"# Soul\nTest soul for {agent}.")
@@ -54,7 +65,7 @@ def _make_persona(root: Path, name: str, agent: str, user: str) -> Path:
 # ---------------------------------------------------------------------------
 
 @pytest_asyncio.fixture
-async def client(personas_root, tmp_path):
+async def client(home_root, tmp_path):
     """HTTPX async test client against the live ASGI app with patched paths."""
     import config
     import persona as persona_mod
@@ -63,13 +74,12 @@ async def client(personas_root, tmp_path):
     sessions_dir.mkdir()
 
     with (
-        patch.object(config.settings, "personas_dir", personas_root),
+        patch.object(config.settings, "home_dir", home_root),
         patch.object(config.settings, "sessions_dir", sessions_dir),
         patch("scheduler.start"),   # don't run APScheduler in tests
         patch("scheduler.stop"),
     ):
-        # Force persona module to re-read patched settings
-        persona_mod._current.set("inara")
+        persona_mod.set_context("scott", "inara")
 
         from main import app
         async with httpx.AsyncClient(