fix: per-persona session/file isolation + onboarding route order

- session_store: store sessions under home/{user}/persona/{name}/session_data/
  instead of the shared cortex/data/sessions/ bucket
- chat endpoints: add user/persona query params to /sessions, /history/*,
  /sessions/*, /note so they resolve the correct persona context
- files router: add user/persona query params to /files and /files/{name}
  so the file browser loads the right persona's files
- app.js: pass user/persona on all session, history, and file fetches;
  move _fileParams to top-level scope so it is available everywhere
- onboarding: fix FastAPI route ordering — register /persona before /{token}
  so the literal path wins and does not get captured as a token value
- ui.py: read Emoji field from IDENTITY.md and inject into CORTEX_CONFIG
  so the header icon reflects each persona's chosen emoji
- .gitignore: exclude home/**/session_data/ (runtime state)
- migrate scott/inara sessions from cortex/data/sessions/ to session_data/

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

.gitignore

@@ -8,6 +8,7 @@ __pycache__/
 
 # Session data (runtime state, not source)
 cortex/data/
+home/**/session_data/
 
 # User credentials and tokens — never commit
 home/**/auth.json