PixDala alpha.40 prepared release candidate

This candidate is based on the verified `v0.4.0-alpha.39` source checkpoint.

Changes: final-participant completion copy and repository-root `AI_HANDOFF.md`; project journals are synchronized so a new chat can reconstruct the verified alpha.39 state and the alpha.40 candidate.

Approved final-participant completion body:

```text
Пора отпустить созданное...
```

The existing button remains:

```text
Развеять мандалу
```

Lifecycle constraint: the server remains authoritative. The last participant starts destruction, other open clients observe `destroying` through revision polling and animate locally, and only the destroyer completes the server-side reset.

Manual QA required before tagging alpha.40: verify the exact final-participant text and button on Telegram Mobile and Desktop; confirm that all previously verified alpha.39 behavior remains unchanged.

Do not deploy this candidate by copying development files directly to the VPS. Replace the corresponding files in the Windows repository, run `npm.cmd run check`, review Git diff, commit and push `main`, create and push the release tag, then deploy with `scripts/deploy-test.sh <tag>`.