feat(roadmap): YAML-driven roadmap + Tailwind UI w/ filters & details modal

- Convert roadmap to YAML:
  - Add data structure: id, priority, title, goal, tags, milestone
  - Add `details` field (supports list or block string); populated initial content
  - Quote scalars and use explicit nulls to avoid YAML parse edge cases
  - Update `updated` date to 2025-08-22

- Flask blueprint + loader:
  - New /roadmap view with section switching (roadmap | backlog | open_questions)
  - Filters: q (search), tag (multi, AND), min_priority, milestone
  - Dataclasses: RoadmapData/RoadmapItem; include `details`
  - `_normalize_details()` to accept string or list, normalize to list[str]
  - Configurable path via `ROADMAP_FILE` (env or defaults)
  - Remove cache layer for simplicity

- UI (Tailwind):
  - `templates/roadmap.html` with responsive cards, tag chips, and filter form
  - Details modal (larger max width, scrollable body) showing ID/goal/priority/tags/milestone
  - Safe JSON payload to modal via `|tojson|forceescape`

- JS:
  - DOM-ready, event-delegated handler for `data-item` buttons
  - Populate modal fields and render multi-paragraph details

- Fixes & polish:
  - Resolved YAML `ScannerError` by quoting strings with `:` and `#`
  - Ensured `details` is passed through route to template and included in button payload
  - Minor styling tweaks for consistency with Tailwind setup

Usage:
- Set `ROADMAP_FILE` if not using default path
- Visit /roadmap and filter via q/tag/min_priority/milestone

app/templates/base.html

@@ -30,6 +30,11 @@
               Home
             </a>
           </li>
+          <li>
+            <a href="{{ url_for('roadmap.roadmap_view') }}">
+              Roadmap
+            </a>
+          </li>
         </ul>
 
         {# Mobile toggle #}
@@ -52,6 +57,11 @@
               Home
             </a>
           </li>
+          <li>
+            <a href="{{ url_for('roadmap.roadmap_view') }}">
+              Roadmap
+            </a>
+          </li>
         </ul>
       </div>
     </div>