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/dashboard.html

@@ -0,0 +1,68 @@
+{% extends "base.html" %}
+
+{% block title %}Dashboard - LinkSync{% endblock %}
+
+{% block content %}
+<div class="dashboard-header">
+    <h1>Dashboard</h1>
+    <p class="welcome-text">Welcome, <span id="current-user"></span></p>
+</div>
+
+<div class="stats-grid">
+    <div class="stat-card">
+        <div class="stat-value" id="link-count">-</div>
+        <div class="stat-label">Total Links</div>
+        <a href="/links" class="stat-link">View all &rarr;</a>
+    </div>
+    <div class="stat-card">
+        <div class="stat-value" id="collection-count">-</div>
+        <div class="stat-label">Collections</div>
+        <a href="/collections" class="stat-link">View all &rarr;</a>
+    </div>
+    <div class="stat-card">
+        <div class="stat-value" id="api-key-count">-</div>
+        <div class="stat-label">API Keys</div>
+        <a href="/api-keys" class="stat-link">Manage &rarr;</a>
+    </div>
+</div>
+
+<div class="quick-actions">
+    <h2>Quick Actions</h2>
+    <div class="action-grid">
+        <a href="/links?action=new" class="action-card">
+            <span class="action-icon">+</span>
+            <span class="action-label">Add Link</span>
+        </a>
+        <a href="/collections?action=new" class="action-card">
+            <span class="action-icon">+</span>
+            <span class="action-label">New Collection</span>
+        </a>
+        <a href="/api-keys?action=new" class="action-card">
+            <span class="action-icon">+</span>
+            <span class="action-label">Create API Key</span>
+        </a>
+        <a href="/docs" target="_blank" class="action-card">
+            <span class="action-icon">&#128736;</span>
+            <span class="action-label">API Documentation</span>
+        </a>
+    </div>
+</div>
+
+<div id="admin-section" class="admin-quick" style="display: none;">
+    <h2>Admin</h2>
+    <div class="action-grid">
+        <a href="/admin" class="action-card">
+            <span class="action-icon">&#128100;</span>
+            <span class="action-label">Manage Users</span>
+        </a>
+        <a href="/admin?action=new-user" class="action-card">
+            <span class="action-icon">+</span>
+            <span class="action-label">Create User</span>
+        </a>
+    </div>
+</div>
+{% endblock %}
+
+{% block extra_js %}
+<script src="/static/js/dashboard.js"></script>
+{% endblock %}