gt spawn beads sync warning is misleading for redirect-based polecats

## Problem

When spawning a polecat, gt spawn shows a warning:
```
Warning: beads sync: exit status 1
```

This is misleading because polecats using the redirect architecture (`.beads/redirect`) share the canonical database at `mayor/rig/.beads/beads.db`. The 'stale beads' indicated by the warning is just git branch divergence (main vs beads-sync), not actual data staleness.

## Expected Behavior

gt spawn should either:
1. Skip the beads sync check for polecats using redirects (they share the canonical DB)
2. Or provide a clearer message like 'beads redirect active, using shared database'

## Reproduction

```bash
gt spawn --issue gt-xxx --rig gastown --create
# Shows 'Warning: beads sync: exit status 1' even though beads are current
```

## Root Cause

spawn.go calls beads sync and treats any non-zero exit as a warning. But with redirects, the polecat doesn't need its own beads - it uses the canonical source via the redirect chain:
```
polecat/.beads/redirect -> ../../.beads -> gastown/.beads/redirect -> mayor/rig/.beads
```

## Fix Options

1. Check for .beads/redirect before calling sync
2. Have bd sync return 0 when redirect is present
3. Suppress the warning in spawn when redirect exists


Agent monitoring and status inference

Agent monitoring with status inference from activity, like PGT.

## Agent Status Enum
```go
type AgentStatus string
const (
    StatusAvailable AgentStatus = "available"
    StatusWorking   AgentStatus = "working"
    StatusThinking  AgentStatus = "thinking"
    StatusBlocked   AgentStatus = "blocked"
    StatusWaiting   AgentStatus = "waiting"
    StatusReviewing AgentStatus = "reviewing"
    StatusIdle      AgentStatus = "idle"
    StatusPaused    AgentStatus = "paused"
    StatusError     AgentStatus = "error"
    StatusOffline   AgentStatus = "offline"
)
```

## Status Sources (priority order)
```go
type StatusSource string
const (
    SourceBossOverride StatusSource = "boss"      // Witness/Mayor sets
    SourceSelfReported StatusSource = "self"      // Agent reports own status
    SourceInferred     StatusSource = "inferred"  // Detected from activity
)
```

## Activity Detection

### Pattern Registry
```go
var activityPatterns = []struct {
    Pattern string
    Status  AgentStatus
}{
    {"Thinking...", StatusThinking},
    {"BLOCKED:", StatusBlocked},
    {"Error:", StatusError},
    // etc
}
```

### Idle Detection
No pane output for N seconds → StatusIdle

### Resource Monitoring (optional)
CPU/memory via os.Process

## New Package
internal/monitoring/
├── types.go      # AgentStatus, StatusReport
├── detector.go   # PatternRegistry, detect from output
├── tracker.go    # Per-agent status tracking
└── idle.go       # Idle timeout detection

## Integration
- Session capture output → monitoring detector
- Status shown in gt status, gt session list

## PGT Reference
gastown-py/src/gastown/monitoring/

## Acceptance Criteria
- [ ] Status enum with 10 states
- [ ] Pattern-based detection from pane output
- [ ] Idle detection with configurable timeout
- [ ] Status visible in CLI output


Merge: gt-xw7b

branch: polecat/morsov
target: main
source_issue: gt-xw7b
rig: gastown


gt spawn should use bd mol run for molecule attachment

Simplify Gas Town to use bd mol run for work tracking.

## Key Insight
Two distinct mechanisms, not duplicative:

| Mechanism | Purpose | Query |
|-----------|---------|-------|
| **Pinned molecule** (bd mol run) | What am I working on? | `bd list --pinned --assignee=me` |
| **Handoff mail** | Context notes for restart | `gt mail read` (self-addressed) |

The handoff is just **mail to yourself** - optional context notes.
The molecule is **the actual work** - required state.

## Current State (Overengineered)
Gas Town has custom attachment system:
- Permanent "Foo Handoff" pinned beads per identity
- AttachMolecule(pinnedBeadID, moleculeID)
- Attachment fields parsed from description
- Separate from beads pinning

## New Model (Simplified)
Use bd mol run directly:

```bash
# Spawn polecat with molecule
bd mol run mol-polecat-work --var issue=gt-xyz
# This: spawns, assigns to caller, pins root, sets in_progress
```

Query current work:
```bash
bd list --pinned --assignee=gastown/furiosa --status=in_progress
```

Handoff context (when needed):
```bash
gt mail send gastown/furiosa -s "Context notes" -m "Was on step 4..."
```

## Changes Required

### Remove from Gas Town
- AttachMolecule() / DetachMolecule()
- AttachmentFields struct and parsing
- GetAttachment() / SetAttachmentFields()
- Permanent pinned handoff beads per identity
- Daemon attachment detection (checkDeaconAttachment)

### Update gt spawn
```go
// Old: custom molecule instantiation + attachment
// New: just call bd mol run
cmd := exec.Command("bd", "mol", "run", protoID, "--var", "issue="+issueID)
```

### Update gt prime / agent context
```go
// Old: find handoff bead, parse attachment
// New: query for pinned molecule
cmd := exec.Command("bd", "list", "--pinned", "--assignee="+identity, "--status=in_progress", "--json")
```

### Update documentation
- Remove handoff bead attachment docs
- Clarify: handoff = mail, molecule = work
- Update CLAUDE.md templates

## Benefits
1. One system for work tracking (beads)
2. Simpler Gas Town code
3. bd mol squash works naturally
4. Handoff is just mail (already works)

## Related
- gt-3x0z: Wisp Molecule Integration
- gt-rana: Patrol System
- gt-lek6: gt rig reset --stale
- gt-ay1r: gt molecule current


Add Deacon heartbeat mechanism

Deacon writes deacon/heartbeat.json on each wake. Go daemon reads it to decide whether to poke. Add heartbeat read/write helpers.