chore(release): stamp v0.51.6 — 5-PR full-sweep batch

5 PRs (1 surface addition, 4 fixes):
- #1717 preserve imported session lineage (@ai-ag2026)
- #1718 preserve Activity count across focus changes (@Michaelyklam, closes #1715)
- #1719 elapsed timer in compact activity (@Michaelyklam, closes #1716)
- #1720 backend tool snippet cap raised to 4000 (@Michaelyklam, closes #1714)
- #1722 suppress stale preserved task lists (@ai-ag2026)

Tests: 4527 → 4537 (+10). Opus: SHIP, 6/6 verification clean.

Co-authored-by: ai-ag2026 <noreply@github.com>
Co-authored-by: Michael Lam <Michaelyklam1@gmail.com>

ROADMAP.md

@@ -2,7 +2,7 @@
 
 > Web companion to the Hermes Agent CLI. Same workflows, browser-native.
 >
-> Last updated: v0.51.5 (May 5, 2026) — 4527 tests collected
+> Last updated: v0.51.6 (May 5, 2026) — 4537 tests collected
 > Test source: `pytest tests/ --collect-only -q`
 > Per-version detail: see [CHANGELOG.md](./CHANGELOG.md)