feat: last-used persona cookie, emoji dropdown, theme support, auth status move

- cx_last_persona cookie set on serve_ui; root/login/help/settings
  redirects use preferred persona from cookie instead of alphabetically first
- /api/personas returns [{name, emoji}] objects; persona switcher dropdown
  renders emoji + name with flex layout and .pd-emoji span
- Help, Settings, Model Registry pages apply localStorage theme on load
  (no flash); CSS variables for dark/light replacing all hardcoded hex values
- Claude CLI auth status moved from prominent chat banner to Anthropic
  provider block in Model Registry — live dot indicator (ok/warn/err)
- Auth banner removed from main chat UI (index.html, app.js, style.css)
- Add Model collapsed into Models section as <details> to shorten page
- Light-mode overrides for provider icons, model badges, ctx-badge, tags
  (Anthropic/Google/local colors now readable in both themes)
- Help page gains table, pre/code, hr styles for HELP.md rendered content

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

cortex/routers/settings.py

@@ -28,6 +28,9 @@ router = APIRouter()
 _STATIC = Path(__file__).parent.parent / "static"
 
 
+_LAST_PERSONA_COOKIE = "cx_last_persona"
+
+
 def _get_session_user(request: Request) -> str | None:
     token = request.cookies.get(COOKIE_NAME)
     if not token:
@@ -38,7 +41,17 @@ def _get_session_user(request: Request) -> str | None:
         return None
 
 
-def _settings_page(username: str, personas: list[str], success: str = "", error: str = "") -> str:
+def _preferred_persona(request: Request, username: str) -> str:
+    names = list_user_personas(username)
+    if not names:
+        return ""
+    cookie_val = request.cookies.get(_LAST_PERSONA_COOKIE, "")
+    if cookie_val in names:
+        return cookie_val
+    return names[0]
+
+
+def _settings_page(username: str, personas: list[str], back_persona: str = "", success: str = "", error: str = "") -> str:
     html = (_STATIC / "settings.html").read_text()
     html = html.replace("{{ username }}", username)
 
@@ -62,7 +75,8 @@ def _settings_page(username: str, personas: list[str], success: str = "", error:
         </li>''' for p in personas
     )
     html = html.replace("{{ persona_items }}", persona_items or "<li><em>No personas yet.</em></li>")
-    back_persona = personas[0] if personas else ""
+    if not back_persona:
+        back_persona = personas[0] if personas else ""
     html = html.replace("{{ back_href }}", f"/{username}/{back_persona}" if back_persona else "/")
     html = html.replace("{{ help_href }}", f"/help?persona={back_persona}" if back_persona else "/help")
     if success:
@@ -78,7 +92,8 @@ async def settings_page(request: Request):
     if not username:
         return RedirectResponse("/login", status_code=302)
     personas = list_user_personas(username)
-    return HTMLResponse(_settings_page(username, personas))
+    back_persona = _preferred_persona(request, username)
+    return HTMLResponse(_settings_page(username, personas, back_persona=back_persona))
 
 
 @router.post("/settings/password", include_in_schema=False)
@@ -93,19 +108,20 @@ async def change_password(
         return RedirectResponse("/login", status_code=302)
 
     personas = list_user_personas(username)
+    back_persona = _preferred_persona(request, username)
 
     if not check_credentials(username, current_password):
-        return HTMLResponse(_settings_page(username, personas, error="Current password is incorrect."))
+        return HTMLResponse(_settings_page(username, personas, back_persona, error="Current password is incorrect."))
 
     if len(new_password) < 8:
-        return HTMLResponse(_settings_page(username, personas, error="New password must be at least 8 characters."))
+        return HTMLResponse(_settings_page(username, personas, back_persona, error="New password must be at least 8 characters."))
 
     if new_password != confirm_password:
-        return HTMLResponse(_settings_page(username, personas, error="New passwords do not match."))
+        return HTMLResponse(_settings_page(username, personas, back_persona, error="New passwords do not match."))
 
     set_password(username, new_password)
     logger.info("password changed: %s", username)
-    return HTMLResponse(_settings_page(username, personas, success="Password updated successfully."))
+    return HTMLResponse(_settings_page(username, personas, back_persona, success="Password updated successfully."))
 
 
 @router.post("/settings/username", include_in_schema=False)
@@ -118,11 +134,12 @@ async def rename_username(
         return RedirectResponse("/login", status_code=302)
 
     personas = list_user_personas(username)
+    back_persona = _preferred_persona(request, username)
     new_username = new_username.strip().lower()
 
     if not _SLUG_RE.match(new_username):
         return HTMLResponse(_settings_page(
-            username, personas,
+            username, personas, back_persona,
             error="Invalid username. Use lowercase letters, digits, _ or - only."))
 
     if new_username == username:
@@ -134,7 +151,7 @@ async def rename_username(
 
     if new_dir.exists():
         return HTMLResponse(_settings_page(
-            username, personas,
+            username, personas, back_persona,
             error=f"Username '{new_username}' is already taken."))
 
     old_dir.rename(new_dir)
@@ -156,6 +173,7 @@ async def save_gemini_key(
         return RedirectResponse("/login", status_code=302)
 
     personas = list_user_personas(username)
+    back_persona = _preferred_persona(request, username)
     gemini_api_key = gemini_api_key.strip()
 
     data = _read_auth(username)
@@ -167,7 +185,7 @@ async def save_gemini_key(
         msg = "Gemini API key removed — using server key."
     _write_auth(username, data)
     logger.info("gemini key updated: %s", username)
-    return HTMLResponse(_settings_page(username, personas, success=msg))
+    return HTMLResponse(_settings_page(username, personas, back_persona, success=msg))
 
 
 @router.post("/settings/persona/rename", include_in_schema=False)
@@ -181,11 +199,12 @@ async def rename_persona(
         return RedirectResponse("/login", status_code=302)
 
     personas = list_user_personas(username)
+    back_persona = _preferred_persona(request, username)
     new_name = new_name.strip().lower()
 
     if not _SLUG_RE.match(new_name):
         return HTMLResponse(_settings_page(
-            username, personas,
+            username, personas, back_persona,
             error="Invalid name. Use lowercase letters, digits, _ or - only."))
 
     if new_name == old_name:
@@ -196,11 +215,11 @@ async def rename_persona(
     new_dir = persona_root / new_name
 
     if not old_dir.exists():
-        return HTMLResponse(_settings_page(username, personas, error=f"Persona '{old_name}' not found."))
+        return HTMLResponse(_settings_page(username, personas, back_persona, error=f"Persona '{old_name}' not found."))
 
     if new_dir.exists():
         return HTMLResponse(_settings_page(
-            username, personas,
+            username, personas, back_persona,
             error=f"A persona named '{new_name}' already exists."))
 
     old_dir.rename(new_dir)