feat(sessions): add stop confirmation, health checks, and tunnel recreation

- Add inline confirmation dialog before stopping instances
- Delete instances from state immediately without page reload
- Add health check polling every 30s for running instances
- Show tunnel error badge when tunnel is unreachable
- Add 'Fix Tunnel' button to recreate broken tunnels
- Update API client with health check and tunnel recreation endpoints

openspec/changes/session-management-fixes/specs/tool-instances/spec.md

@@ -0,0 +1,46 @@
+## MODIFIED Requirements
+
+### Requirement: Tool Lifecycle
+
+The system SHALL manage tool lifecycle operations including tunnel recreation.
+
+#### Scenario: Stop tool
+- GIVEN a running tool instance
+- WHEN the user stops it
+- THEN `docker compose stop` is executed
+- AND the cloudflared tunnel process is terminated
+- AND status is updated to "stopped"
+
+#### Scenario: Start tool
+- GIVEN a stopped tool instance
+- WHEN the user starts it
+- THEN `docker compose start` is executed
+- AND a new temporary Cloudflare tunnel is created
+- AND status is updated to "running"
+
+#### Scenario: Recreate tunnel
+- GIVEN a running tool instance with a broken tunnel
+- WHEN the user requests tunnel recreation
+- THEN the existing cloudflared process is terminated
+- AND a new temporary Cloudflare tunnel is created
+- AND the instance URL is updated
+- AND the instance shows as healthy
+
+## ADDED Requirements
+
+### Requirement: Tunnel Health Check
+
+The system SHALL check tunnel health for running instances.
+
+#### Scenario: Healthy tunnel check
+- GIVEN a running instance with an active tunnel
+- WHEN the health check runs
+- THEN the tunnel URL responds with HTTP 2xx
+- AND the instance is marked as healthy
+
+#### Scenario: Broken tunnel check
+- GIVEN a running instance with a broken tunnel
+- WHEN the health check runs
+- THEN the tunnel URL does not respond with HTTP 2xx
+- AND the instance is marked with tunnel_error
+- AND a "Recreate Tunnel" button is shown