feat: Add AI-native observability and self-recovery module

[nfebe]

Problem

The agent has no observability or recovery module. Four gaps:

1. No deployment health. Nothing tracks whether a deployment's containers
   are running. Agent health is independent of deployment state, so a dead
   deployment produces no signal.
2. No recovery. On startup the agent starts only the file watcher and API
   server with no deployment reconcile (cmd/agent/main.go:21-83); on shutdown
   it stops only the API server. Recovery after a host or Docker daemon restart
   depends entirely on each container's restart: policy
   (agent/templates/*/docker-compose.yml). When that does not fire (compose
   file without it, missing external network, image that will not pull at boot),
   deployments stay down with no auto-heal.
3. No notifications. No mechanism exists to alert an operator to anything.
   Email is used only for registry credentials and certbot.
4. Resource visibility is thin. Host CPU and memory are read point-in-time
   (internal/system/stats.go); there is no per-container monitoring and no
   spike detection.

Constraint: recovery must not restart deployments the user intentionally
stopped. Reconcile against tracked desired state, not a blind up of every
directory.

Why it matters

A reboot or a resource spike becomes a silent outage. The first signal is a
user reporting the site is down.

Proposal

One observability and recovery module that reuses the existing AI action engine.

1. Health monitoring. Poll per-deployment container state (running / exited
   / restarting, health, exit codes), expose via API.
2. Resource monitoring. Extend internal/system/stats.go with per-container
   CPU and memory and configurable spike thresholds.
3. Notifications. A pluggable channel subsystem, email first, interface open
   for webhook and others. Notify on ill-health, resource spikes, and
   recovery-from-shutdown events.
4. AI-native recovery. At boot and on detected ill-health, reconcile
   deployments to desired state. Drive remediation through the existing
   service_action suggestion engine (internal/ai/suggestions.go:
   restart / rebuild / pull) so the recovery is diagnosis-led, not blind.
   Emit a recovery event when deployments are brought back after a restart.

Action

• Per-deployment health checker exposed via API
• Per-container resource monitoring with configurable spike thresholds
• Notification subsystem: email channel plus a pluggable interface for more
• Boot-time and on-failure reconcile to desired state; skip intentionally-stopped deployments
• Emit and notify recovery events (for example "recovered N deployments after host restart")
• Route remediation through the AI service_action engine

Acceptance criteria

• After a host reboot, deployments self-recover without manual intervention and a recovery notification is sent.
• Operators are notified on deployment ill-health and on resource spikes.

[nfebe]

Shipped in #165 and flatrun/ui#78. Tracked under Albacore #158. Non-blocking follow-ups (watcher lock, plaintext notification secrets, notification HTTP tests, set_auto_restart scoping) are listed there.