feat: 404 pages → redirect to /workspaces

- main.py: @app.exception_handler(404) → RedirectResponse(/workspaces)
- dashboard.py: page_detail 404 → RedirectResponse(/workspaces)
- tests: test_styled_404_page → 302 redirect
- API paths (containing /api) still get JSON 404, not redirect
- 143 tests passent

app/main.py

@@ -152,10 +152,10 @@ body{font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',sans-serif;backgrou
 
 @app.exception_handler(404)
 async def not_found_handler(request: Request, exc):
-    """Styled 404 page matching the FlowDeck dark theme."""
+    """Redirect 404 HTML pages to /workspaces. API routes still get JSON."""
-    from fastapi.responses import HTMLResponse
+    # Preserve JSON 404 for all API-like paths (including /db/xxx/api)
-    # API routes should get JSON, not HTML
+    if "/api" in request.url.path:
-    if request.url.path.startswith("/api/") or request.url.path.startswith("/board/api/"):
         from fastapi.responses import JSONResponse
         return JSONResponse({"detail": "Not found"}, status_code=404)
-    return HTMLResponse(NOT_FOUND_HTML, status_code=404)
+    from fastapi.responses import RedirectResponse
+    return RedirectResponse("/workspaces", status_code=302)

tests/test_app.py

@@ -1950,11 +1950,10 @@ def test_create_page_defaults_to_untitled(client):
 
 
 def test_styled_404_page(client):
-    """Unknown routes return a styled 404 HTML page."""
+    """Unknown routes redirect to /workspaces."""
     resp = client.get("/this-does-not-exist-xyz", follow_redirects=False)
-    assert resp.status_code == 404
+    assert resp.status_code == 302
-    assert "404" in resp.text
+    assert resp.headers.get("location") == "/workspaces"
-    assert "FlowDeck" in resp.text
 
 
 def test_api_404_returns_json(client):