chore(release): stamp v0.51.8 — 7-PR full-sweep batch + Opus follow-up + test-isolation fix

Constituent PRs:
- #1725 (@Michaelyklam) — simplify compact Activity row summary
- #1726 (@Michaelyklam) — delegate generic provider catalogs to Hermes CLI (slice of #1240)
- #1727 (@Michaelyklam) — link Claude Code OAuth in onboarding (closes #1362)
- #1728 (@starship-s) — preserve profile context when starting chats
- #1729 (@Michaelyklam) — persist compact Activity disclosure state
- #1730 (@Michaelyklam) — prevent sticky sidebar hover drag state
- #1732 (@Sanjays2402) — unpin scroll on small upward motion during streaming (closes #1731)

Plus 2 in-stage absorbed fixes:
- test-isolation fix: monkeypatch.setattr(config, 'cfg', X) survives PR #1728's
  path/mtime-aware get_config() reload. Mandatory before tag (Opus stage-302).
- Opus SHOULD-FIX #1: _lastScrollTop reset on session switch (#1732 follow-up).

Tests: 4537 → 4584 passing (+47). 0 regressions. Full suite ~128s. Stably green.

Pre-release verification:
- All 7 PRs CI-green individually + rebased onto master
- pytest 4584 passed, 0 failed (multiple runs)
- node -c clean on all 4 modified .js files
- 11/11 browser API endpoints PASS on isolated port 8789
- 20 QA tests via webui_qa_agent.sh PASS
- Opus advisor: SHIP, 5/5 verification clean, 0 MUST-FIX, 1 SHOULD-FIX absorbed
  (_lastScrollTop reset), 1 SHOULD-FIX deferred (#1736 — _clear_anthropic_env_values
  race, onboarding-time-only)

Closes #1362, #1731.

ROADMAP.md

@@ -2,7 +2,7 @@
 
 > Web companion to the Hermes Agent CLI. Same workflows, browser-native.
 >
-> Last updated: v0.51.7 (May 5, 2026) — 4550 tests collected — single-PR docs+dx (#1695: AIAgent not available diagnostic)
+> Last updated: v0.51.8 (May 6, 2026) — 4584 tests collected — 7-PR full-sweep batch (#1725-1730, #1732)
 > Test source: `pytest tests/ --collect-only -q`
 > Per-version detail: see [CHANGELOG.md](./CHANGELOG.md)