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/ui.py

@@ -56,12 +56,26 @@ def _set_cookie(response: Response, username: str) -> None:
     )
 
 
+_LAST_PERSONA_COOKIE = "cx_last_persona"
+
+
 def _first_persona(username: str) -> str | None:
     """Return the first available persona for a user, or None."""
     names = list_user_personas(username)
     return names[0] if names else None
 
 
+def _preferred_persona(request: Request, username: str) -> str | None:
+    """Return the last-visited persona from cookie if valid, else the first available."""
+    names = list_user_personas(username)
+    if not names:
+        return None
+    cookie_val = request.cookies.get(_LAST_PERSONA_COOKIE, "")
+    if cookie_val in names:
+        return cookie_val
+    return names[0]
+
+
 # ---------------------------------------------------------------------------
 # Favicon — default sparkle; persona pages override via JS
 # ---------------------------------------------------------------------------
@@ -85,7 +99,7 @@ async def root(request: Request):
     user = _get_session_user(request)
     if not user:
         return RedirectResponse("/login", status_code=302)
-    persona = _first_persona(user)
+    persona = _preferred_persona(request, user)
     if not persona:
         return HTMLResponse("<h1>No personas configured for your account.</h1>", status_code=500)
     return RedirectResponse(f"/{user}/{persona}", status_code=302)
@@ -100,7 +114,7 @@ async def login_page(request: Request):
     user = _get_session_user(request)
     if user:
         # Already logged in — redirect home
-        persona = _first_persona(user)
+        persona = _preferred_persona(request, user)
         if persona:
             return RedirectResponse(f"/{user}/{persona}", status_code=302)
     return HTMLResponse((_STATIC / "login.html").read_text())
@@ -254,7 +268,16 @@ async def api_personas(request: Request) -> dict:
     if not user:
         from fastapi import HTTPException
         raise HTTPException(status_code=401, detail="Not authenticated")
-    return {"user": user, "personas": list_user_personas(user)}
+    personas_with_emoji = []
+    for p in list_user_personas(user):
+        emoji = "✨"
+        identity_path = persona_path(user, p) / "IDENTITY.md"
+        if identity_path.exists():
+            m = re.search(r"\|\s*Emoji\s*\|\s*(.+?)\s*\|", identity_path.read_text())
+            if m:
+                emoji = m.group(1).strip()
+        personas_with_emoji.append({"name": p, "emoji": emoji})
+    return {"user": user, "personas": personas_with_emoji}
 
 
 @router.get("/{username}/{persona}", include_in_schema=False)
@@ -288,4 +311,6 @@ async def serve_ui(username: str, persona: str, request: Request):
         f'{{user: "{username}", persona: "{persona}", emoji: "{emoji}"}};</script>'
     )
     html = html.replace("</head>", f"{config_tag}\n</head>", 1)
-    return HTMLResponse(html)
+    resp = HTMLResponse(html)
+    resp.set_cookie(_LAST_PERSONA_COOKIE, persona, max_age=365 * 86400, httponly=False, samesite="lax")
+    return resp