Immediate daemon notification on lifecycle request

When gt handoff sends a lifecycle request to the daemon (via bd mail send deacon/), the daemon only discovers it on its next heartbeat poll (every 5 min). Workers wait unnecessarily for retirement.

## Current Behavior
1. Worker runs gt handoff
2. Lifecycle mail sent to deacon/ via beads
3. Worker blocks waiting for retirement
4. Daemon heartbeat runs (up to 5 min later)
5. Daemon processes lifecycle request and kills session

## Expected Behavior
Lifecycle requests should be processed immediately, not on poll interval.

## Proposed Solutions

### Option A: SIGUSR1 Signal (simplest)
1. Add SIGUSR1 handler in daemon that calls ProcessLifecycleRequests()
2. gt handoff reads daemon.pid and sends SIGUSR1 after mail send

### Option B: Unix Socket
1. Daemon listens on ~/gt/daemon/lifecycle.sock
2. gt handoff connects and sends 'process' message

### Option C: Watchfile + fsnotify
1. gt handoff touches ~/gt/daemon/lifecycle.trigger
2. Daemon uses fsnotify to detect and process

Recommend Option A for simplicity.

## Affected Files
- internal/daemon/daemon.go - add signal handler
- internal/cmd/handoff.go - send signal after mail


Per-rig beads repo configuration

Add per-rig beads configuration to rig config schema.

## Config Schema

In each rig's config.json:

```json
{
  "version": 1,
  "name": "wyvern",
  "git_url": "https://github.com/steveyegge/wyvern",
  "beads": {
    "repo": "local",    // "local" | "<path>" | "<git-url>"
    "root": null,       // Override bd --root (optional)
    "prefix": "wyv"     // Issue prefix for this rig
  }
}
```

## Repo Options

| Value | Meaning | Use Case |
|-------|---------|----------|
| `"local"` | Use project's `.beads/` | Own projects, full commit access |
| `"<path>"` | Use beads at path | OSS contributions |
| `"<git-url>"` | Clone and use repo | Team shared beads |

## Environment Injection

When spawning polecats, Gas Town sets:
```bash
export BEADS_ROOT="<resolved-path>"
```

## Resolution Logic

```go
func ResolveBeadsRoot(rigConfig *RigConfig, rigPath string) (string, error) {
    beads := rigConfig.Beads
    switch {
    case beads.Root != "":
        return beads.Root, nil
    case beads.Repo == "local" || beads.Repo == "":
        return filepath.Join(rigPath, ".beads"), nil
    case strings.HasPrefix(beads.Repo, "/"):
        return beads.Repo, nil
    case strings.Contains(beads.Repo, "://"):
        return cloneAndResolve(beads.Repo)
    default:
        return filepath.Join(rigPath, beads.Repo), nil
    }
}
```

## Backwards Compatibility

If `beads` section missing, assume `"repo": "local"`.


request-shutdown

Send shutdown request to Witness.
Wait for termination.

The polecat is now ready to be cleaned up.
Do not exit directly - wait for Witness to kill the session.

Depends: generate-summary