feat: add web UI with login, CRUD, admin, and API key management

- Add login page with JWT authentication
- Add dashboard with stats and quick actions
- Add links management page (full CRUD with search)
- Add collections management page
- Add API key management page with copy-to-clipboard
- Add admin user management page (admin only)
- Fix UUID type mismatches across all endpoints
- Add updated_at column to api_keys and audit_log in schema.sql
- Fix DB_PASSWORD default in docker-compose.yml
- Add PyJWT to requirements.txt
- Fix API docs URL (/docs instead of /api/docs)
- Improve JS error handling (show actual messages)
- Rewrite conftest.py with proper DB lifecycle management
- Add 42 new integration tests (84 total, all passing)
  - test_admin.py: 15 tests for admin endpoints
  - test_auth_extended.py: 9 tests for API key CRUD
  - test_tags.py: 12 tests for tag endpoints
  - test_sync.py: 6 tests for sync endpoints

LinkSyncServer/templates/collections.html

@@ -0,0 +1,68 @@
+{% extends "base.html" %}
+
+{% block title %}Collections - LinkSync{% endblock %}
+
+{% block content %}
+<div class="page-header">
+    <h1>Collections</h1>
+    <button class="btn btn-primary" id="new-collection-btn">+ New Collection</button>
+</div>
+
+<div id="collections-list" class="collections-grid">
+    <div class="loading">Loading collections...</div>
+</div>
+
+<div id="collection-modal" class="modal" style="display: none;">
+    <div class="modal-overlay"></div>
+    <div class="modal-content">
+        <div class="modal-header">
+            <h2 id="collection-modal-title">Create Collection</h2>
+            <button class="modal-close" id="collection-modal-close">&times;</button>
+        </div>
+        <form id="collection-form">
+            <input type="hidden" id="collection-id">
+            <div class="form-group">
+                <label for="collection-name">Name *</label>
+                <input type="text" id="collection-name" required>
+            </div>
+            <div class="form-group">
+                <label for="collection-description">Description</label>
+                <textarea id="collection-description" rows="2"></textarea>
+            </div>
+            <div class="form-group">
+                <label for="collection-type">Type</label>
+                <select id="collection-type">
+                    <option value="static">Static (manual links)</option>
+                    <option value="dynamic">Dynamic (query-based)</option>
+                </select>
+            </div>
+            <div class="form-group checkbox-group">
+                <label>
+                    <input type="checkbox" id="collection-public">
+                    Public
+                </label>
+            </div>
+            <div class="form-actions">
+                <button type="button" class="btn btn-secondary" id="collection-cancel-btn">Cancel</button>
+                <button type="submit" class="btn btn-primary" id="collection-save-btn">Save</button>
+            </div>
+        </form>
+    </div>
+</div>
+
+<div id="delete-collection-modal" class="modal" style="display: none;">
+    <div class="modal-overlay"></div>
+    <div class="modal-content modal-sm">
+        <h2>Delete Collection</h2>
+        <p>Are you sure you want to delete this collection? This action cannot be undone.</p>
+        <div class="form-actions">
+            <button class="btn btn-secondary" id="delete-collection-cancel-btn">Cancel</button>
+            <button class="btn btn-danger" id="confirm-delete-collection-btn">Delete</button>
+        </div>
+    </div>
+</div>
+{% endblock %}
+
+{% block extra_js %}
+<script src="/static/js/collections-page.js"></script>
+{% endblock %}