refactor: move webapp from /user/page to /app

Simplified the webapp routing structure by consolidating the admin UI
to a single clean endpoint.

Changes:
- Moved webapp from /user/page to /app (root of mount)
- Removed /user JSON endpoint (no longer needed)
- Updated mount point from /user to /app in app.py
- Updated all route path checks (3 locations)
- Updated OAuth redirects to point to /app
- Updated all HTMX endpoint references
- Updated documentation (ADR-007, CHANGELOG)
- Added redirect from /app to /app/ for trailing slash handling

New Route Structure:
- /app - Main webapp (HTML UI with tabs)
- /app/revoke - Revoke background access
- /app/webhooks - Webhook management UI
- /app/webhooks/enable/{preset_id} - Enable webhook preset
- /app/webhooks/disable/{preset_id} - Disable webhook preset

Breaking Change: Existing bookmarks to /user or /user/page will no longer work.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

nextcloud_mcp_server/auth/webhook_routes.py

@@ -32,7 +32,7 @@ def _get_storage(request: Request):
     Returns:
         RefreshTokenStorage instance or None
     """
-    # Try browser_app state first (for /user routes)
+    # Try browser_app state first (for /app routes)
     storage = getattr(request.app.state, "storage", None)
 
     # Try oauth_context if in OAuth mode
@@ -289,7 +289,7 @@ async def webhook_management_pane(request: Request) -> HTMLResponse:
                 status_badge = f'<span style="color: #4caf50; font-weight: bold;">✓ Enabled ({num_webhooks} webhooks)</span>'
                 action_button = f"""
                 <button
-                    hx-delete="/user/webhooks/disable/{preset_id}"
+                    hx-delete="/app/webhooks/disable/{preset_id}"
                     hx-target="#preset-{preset_id}"
                     hx-swap="outerHTML"
                     class="button"
@@ -301,7 +301,7 @@ async def webhook_management_pane(request: Request) -> HTMLResponse:
                 status_badge = '<span style="color: #999;">Not Enabled</span>'
                 action_button = f"""
                 <button
-                    hx-post="/user/webhooks/enable/{preset_id}"
+                    hx-post="/app/webhooks/enable/{preset_id}"
                     hx-target="#preset-{preset_id}"
                     hx-swap="outerHTML"
                     class="button button-primary">
@@ -429,7 +429,7 @@ async def enable_webhook_preset(request: Request) -> HTMLResponse:
                     <div><span style="color: #4caf50; font-weight: bold;">✓ Enabled ({num_webhooks} webhooks)</span></div>
                     <div>
                         <button
-                            hx-delete="/user/webhooks/disable/{preset_id}"
+                            hx-delete="/app/webhooks/disable/{preset_id}"
                             hx-target="#preset-{preset_id}"
                             hx-swap="outerHTML"
                             class="button"
@@ -520,7 +520,7 @@ async def disable_webhook_preset(request: Request) -> HTMLResponse:
                     <div><span style="color: #999;">Not Enabled</span></div>
                     <div>
                         <button
-                            hx-post="/user/webhooks/enable/{preset_id}"
+                            hx-post="/app/webhooks/enable/{preset_id}"
                             hx-target="#preset-{preset_id}"
                             hx-swap="outerHTML"
                             class="button button-primary">