docs: add GET /:id endpoint documentation and update implementation plan

Add comprehensive documentation for GET /api/saved-filters/:id endpoint
including Bruno API collection, developer API docs, user documentation,
and implementation plan with frontend integration phase.

Bruno API Collection (bruno/saved-filters/Get Saved Filter By ID.yml):
- New Bruno request file for GET /:id endpoint
- Includes comprehensive documentation with examples
- Documents all status codes (200, 400, 401, 404)
- Provides example curl commands and use cases
- Uses variable placeholders ({{base_url}}, {{filter_id}})
- Follows existing Bruno YAML patterns

API Documentation (docs/developer/api/saved-filters/index.md):
- Added GET /api/saved-filters/:id endpoint documentation
- Example request with UUID parameter
- Example response showing filter object structure
- Error responses documented (400, 401, 404)
- Use cases: Mobile apps, SPAs, editing, verification

User Documentation (docs/user/library-browsing.md):
- Updated "Loading Saved Filters" section
- Removed "feature coming soon" language
- Added step-by-step instructions for loading filters
- Added tips section with visual indicators
- Added "Managing Saved Filters" section
- Added "Common Use Cases" (genre, author, series)
- Emphasizes instant feedback (no page reload)

Implementation Plan (GET_SAVED_FILTER_BY_ID_IMPLEMENTATION.md):
- Added Phase 7: User Documentation Update
- Added Phase 8: Frontend Integration (bookshelf.ts)
  - Shows loadFilter() implementation
  - Hybrid Alpine.js + HTMX approach
  - Maintains SSR-first principles
  - API call on user interaction, not page load
  - Populates hidden form fields
  - Triggers HTMX to apply filter
- Updated Summary of Changes: 7 files, ~344 lines
- Updated Checklist with frontend and user docs tasks
- Added frontend testing tasks

SSR-First Compliance:
- Initial page load: Server renders everything (no API calls)
- User interaction only: API called when user clicks filter
- No async x-init data fetching
- Progressive enhancement maintained

Documentation Structure:
- Developer docs: API reference for integration
- User docs: Step-by-step usage instructions
- Bruno: API contract testing
- Implementation plan: Complete development guide

All documentation follows established patterns and includes examples.

docs/user/library-browsing.md

@@ -12,8 +12,49 @@ The bookshelf page allows you to save custom filter presets for quick access.
 
 ### Loading Saved Filters
 
-After saving filters, you can quickly load them from the saved filters dropdown (feature coming soon). For now, saved filters persist across page refreshes.
+After saving filters, you can quickly load them from the saved filters dropdown:
 
-### Filter Privacy
+1. Click the **📋 Saved Filters** button (next to the Save Filter button)
+2. Select a filter from the dropdown list
+3. The filter values are automatically applied to the form
+4. Your books are instantly filtered to show matching results
+
+**Tips:**
+- Saved filters appear in the dropdown with their names
+- Hover over a filter to see a delete button (🗑️)
+- Click a filter name to apply it instantly
+- Filters are applied without page reload (instant feedback)
+
+### Managing Saved Filters
+
+**View Saved Filters:**
+- Saved filters are displayed in the dropdown
+- Each filter shows its name (e.g., "My Sci-Fi Books")
+
+**Delete a Filter:**
+1. Click the **📋 Saved Filters** button
+2. Hover over the filter you want to delete
+3. Click the **🗑️** delete button
+4. Confirm deletion
+5. The filter is removed from your list
+
+**Filter Privacy:**
 
 Saved filters are **private to your account**. Other users cannot see or modify your filters.
+
+### Common Use Cases
+
+**Reading by Genre:**
+1. Filter by genre: "Science Fiction"
+2. Save as "Sci-Fi Books"
+3. Quickly access all your sci-fi collection anytime
+
+**Author Collections:**
+1. Filter by author: "Isaac Asimov"
+2. Save as "Asimov Books"
+3. Switch between different author collections instantly
+
+**Series Tracking:**
+1. Filter by series: "Foundation"
+2. Save as "Foundation Series"
+3. Track your progress through a series