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/api/endpoints/admin.py

@@ -5,7 +5,7 @@ LinkSyncServer - Admin Endpoints
 import uuid
 from typing import List, Optional
 
-from fastapi import APIRouter, HTTPException, Query, status
+from fastapi import APIRouter, Depends, HTTPException, Query, status
 from pydantic import BaseModel, EmailStr, Field
 
 from api.endpoints.auth import hash_password, require_admin
@@ -34,11 +34,18 @@ class SettingsUpdate(BaseModel):
     cors_origins: Optional[str] = None
 
 
+def parse_uuid(id_str: str):
+    try:
+        return uuid.UUID(id_str) if isinstance(id_str, str) else id_str
+    except (ValueError, AttributeError):
+        return None
+
+
 @router.get("/users", response_model=List[dict])
 async def list_users(
     limit: int = Query(20, le=100, ge=1),
     offset: int = Query(0, ge=0),
-    current_admin: dict = require_admin,
+    current_admin: dict = Depends(require_admin),
 ):
     db = get_session()
     try:
@@ -51,7 +58,7 @@ async def list_users(
 @router.post("/users", response_model=dict, status_code=status.HTTP_201_CREATED)
 async def create_user(
     data: UserCreate,
-    current_admin: dict = require_admin,
+    current_admin: dict = Depends(require_admin),
 ):
     db = get_session()
     try:
@@ -62,7 +69,7 @@ async def create_user(
             raise HTTPException(status_code=400, detail="Username or email already exists")
 
         user = User(
-            id=str(uuid.uuid4()),
+            id=uuid.uuid4(),
             username=data.username,
             email=data.email,
             password_hash=hash_password(data.password),
@@ -80,11 +87,14 @@ async def create_user(
 @router.get("/users/{user_id}", response_model=dict)
 async def get_user(
     user_id: str,
-    current_admin: dict = require_admin,
+    current_admin: dict = Depends(require_admin),
 ):
     db = get_session()
     try:
-        user = db.query(User).filter(User.id == user_id).first()
+        parsed_id = parse_uuid(user_id)
+        if parsed_id is None:
+            raise HTTPException(status_code=404, detail="User not found")
+        user = db.query(User).filter(User.id == parsed_id).first()
         if not user:
             raise HTTPException(status_code=404, detail="User not found")
         return user.to_dict()
@@ -96,11 +106,14 @@ async def get_user(
 async def update_user(
     user_id: str,
     data: UserUpdate,
-    current_admin: dict = require_admin,
+    current_admin: dict = Depends(require_admin),
 ):
     db = get_session()
     try:
-        user = db.query(User).filter(User.id == user_id).first()
+        parsed_id = parse_uuid(user_id)
+        if parsed_id is None:
+            raise HTTPException(status_code=404, detail="User not found")
+        user = db.query(User).filter(User.id == parsed_id).first()
         if not user:
             raise HTTPException(status_code=404, detail="User not found")
 
@@ -121,11 +134,14 @@ async def update_user(
 @router.delete("/users/{user_id}", response_model=dict)
 async def delete_user(
     user_id: str,
-    current_admin: dict = require_admin,
+    current_admin: dict = Depends(require_admin),
 ):
     db = get_session()
     try:
-        user = db.query(User).filter(User.id == user_id).first()
+        parsed_id = parse_uuid(user_id)
+        if parsed_id is None:
+            raise HTTPException(status_code=404, detail="User not found")
+        user = db.query(User).filter(User.id == parsed_id).first()
         if not user:
             raise HTTPException(status_code=404, detail="User not found")
         if user.username == current_admin.get("username"):
@@ -139,7 +155,7 @@ async def delete_user(
 
 
 @router.get("/stats", response_model=dict)
-async def get_system_stats(current_admin: dict = require_admin):
+async def get_system_stats(current_admin: dict = Depends(require_admin)):
     db = get_session()
     try:
         return {
@@ -159,7 +175,7 @@ async def get_audit_log(
     offset: int = Query(0, ge=0),
     entity_type: Optional[str] = Query(None),
     action: Optional[str] = Query(None),
-    current_admin: dict = require_admin,
+    current_admin: dict = Depends(require_admin),
 ):
     db = get_session()
     try:
@@ -171,14 +187,14 @@ async def get_audit_log(
         logs = query.order_by(AuditLog.created_at.desc()).offset(offset).limit(limit).all()
         return [
             {
-                "id": log.id,
-                "user_id": log.user_id,
+                "id": str(log.id),
+                "user_id": str(log.user_id) if log.user_id else None,
                 "action": log.action,
                 "entity_type": log.entity_type,
-                "entity_id": log.entity_id,
+                "entity_id": str(log.entity_id) if log.entity_id else None,
                 "old_value": log.old_value,
                 "new_value": log.new_value,
-                "ip_address": log.ip_address,
+                "ip_address": str(log.ip_address) if log.ip_address else None,
                 "created_at": log.created_at.isoformat() if log.created_at else None,
             }
             for log in logs