feat(factory-health): bootstrap .factory/.gitignore so dispatcher logs / tmp / locks don't accumulate in the orphan branch

## Summary

After `/vsdd-factory:factory-health` mounts the `.factory/` worktree on the `factory-artifacts` orphan branch, no `.gitignore` is bootstrapped inside that worktree. Transient state — `dispatcher-internal-*.jsonl` from factory-obs, possible lock files, tmp scratch, OTEL temp data — accumulates as untracked content inside the orphan branch's worktree.

Without an ignore policy:
- `git status` inside `.factory/` always shows `logs/` as untracked, even when nothing intentional changed.
- If a future state-manager run does `git add -A`, transient logs get committed permanently to `factory-artifacts`.
- The signal-to-noise ratio of `git status` in the worktree is terrible.

## Repro

Fresh project, run `/vsdd-factory:factory-health`. Worktree mounts at `.factory/`. After any factory-obs activity:

```
$ cd .factory && git status --porcelain
?? logs/
?? logs/dispatcher-internal-2026-06-23.jsonl
```

No `.gitignore`, no policy.

## Proposed fix

Factory-health step 5 (directory structure) should also create `.factory/.gitignore`:

```gitignore
# Auto-generated by /vsdd-factory:factory-health
# Dispatcher / runtime logs are not artifacts — keep out of factory-artifacts commits
logs/
*.log

# Lock files
*.lock
.factory-lock
.factory-health-in-progress

# Temp / scratch
tmp/
.tmp/
*.tmp
*.swp

# OS noise
.DS_Store
Thumbs.db

# Editor noise
.vscode/
.idea/
*~

# Local-only OTEL / collector state
.otel-state/
```

Commit this `.gitignore` to `factory-artifacts` as part of the initial bootstrap (alongside STATE.md and the `.gitkeep` files).

## Acceptance criteria

- [ ] Factory-health bootstraps `.factory/.gitignore` on first run.
- [ ] `logs/` and other transient state are ignored inside the orphan-branch worktree.
- [ ] Subsequent `state-manager` commits do not pick up transient log files.
- [ ] Existing projects can run `/vsdd-factory:factory-health` and have the `.gitignore` retroactively created (idempotent).

## Found during

`/vsdd-factory:factory-health` on `switchboard-blue` (2026-06-23, vsdd-factory@1.0.0-rc.21). After mount + first dispatcher activity, `logs/dispatcher-internal-2026-06-23.jsonl` was untracked inside the worktree with no `.gitignore` policy. The first commit I made deliberately did NOT include `logs/` — but a future `git add -A` operation by state-manager would silently commit it.

## Related

- (this session, filed) #206 — dispatcher race + filed earlier suggestion that dispatcher-internal logs belong outside the user's repo entirely. This issue is the BACKSTOP if that doesn't happen.