chore(release): stamp v0.51.13 — single-PR composer UX (#1758)

Constituent PR:
- #1758 (@nesquena-hermes) — feat(composer): click pasted/attached image
  thumbnails to lightbox-zoom them. Refs #1733. Companion Mac PR
  hermes-webui/hermes-swift-mac#74 for sequential-paste filename uniqueness.

Independent review: @nesquena APPROVED with exhaustive headless-Chrome
behavioural harness verifying all 4 click paths (thumb-image, ×-on-image,
×-on-audio, audio-element). Pre-fix verification confirmed 4/5 of the new
tests catch regressions to the previous state.

Opus advisor: SHIP, all 6 verification questions clean. One non-blocking
nit absorbed in-release: wrap .attach-thumb:hover in @media (hover: hover)
for iPad sticky-hover hygiene (3-LOC defensive cleanup).

Tests: 4637 → 4642 collected (+5). 4630 passed, 9 skipped, 3 xpassed,
0 failed.

Pre-release verification:
- pytest 4630 passed, 0 failed
- node -c clean on static/ui.js
- 11/11 browser API endpoints PASS
- Pre-stamp re-fetch: PR head still matches local rebase
- Opus advisor: SHIP, 0 MUST-FIX

Refs #1733.

ROADMAP.md

@@ -2,7 +2,7 @@
 
 > Web companion to the Hermes Agent CLI. Same workflows, browser-native.
 >
-> Last updated: v0.51.12 (May 6, 2026) — 4632 tests collected — 3-PR full-sweep batch (#1746, #1752, #1753)
+> Last updated: v0.51.13 (May 6, 2026) — 4642 tests collected — single-PR composer UX (#1758)
 > Test source: `pytest tests/ --collect-only -q`
 > Per-version detail: see [CHANGELOG.md](./CHANGELOG.md)