chore(release): 0.8.1

[willytop8]

Version bump and changelog for 0.8.1.

Delivers the two merged changes that affect what npm publishes:

• fix(goal-loop): resume auto-continue after session compaction #58 — fix auto-continue stalling after session compaction. Contributed by @harryzhou2000.
• chore(deps): bump zod from 4.1.8 to 4.4.3 #52 — zod 4.1.8 → 4.4.3, the package's only runtime dependency.

#37 (GitHub Actions bumps) and #44 (TypeScript 5.9.3 → 7.0.2) are CI and dev-only and do not reach the published package.

npm run release:check passes end to end:

• 385/385 tests
• type contract (NodeNext + Bundler)
• 67/67 critical mutants killed
• behavior benchmark, source and packed-artifact smokes, clean-install tool registration
• npm audit --omit=dev --audit-level=high — 0 vulnerabilities
• packs as opencode-goal-plugin-0.8.1.tgz