feat(achievements): add export endpoint and agent summary (#18472)

[frirenai]

What does this PR do?

Implements the export & agent-communication workstream from the achievements upgrades tracking issue (#18472, spec in closed PR #18151). Achievements are currently trapped in state.json and the dashboard tab; this adds the two surfaces the spec defines for getting them out:

• GET /api/plugins/hermes-achievements/export?format=json|markdown|svg&state=... — renders the current snapshot as machine-readable JSON, a README-pasteable Markdown badge table (shields.io badges + ██░░ progress bars, unlocked badges by default), or an SVG badge sheet with tier-colored markers. Unknown formats return a 400 JSON error instead of guessing.
• GET /api/plugins/hermes-achievements/achievements/summary — the compact agent profile from the spec (strengths, gaps, top_tier, unlocked_ids, unlocked_count, total_count, session/tool totals), small enough for context injection.
• agent_summary.json — the same payload is written next to state.json after every finished scan (best-effort, never fails the scan) and removed on /reset-state, so agents and external tools can read the profile without the dashboard running.

Scope notes, per the issue's guidance that the four workstreams land as separate PRs:

• filter_and_sort_achievements() is added as the minimal state-filter seam the export formatters need; the filtering/sorting workstream can extend the same function with category/sort_by/limit without rework.
• The hermes achievements CLI and TUI panel workstream is intentionally not included here; the CLI's export path can delegate to these formatters when it lands.

Two small deviations from the spec's reference snippets, both deliberate:

• The spec's agent_summary.json write used a hardcoded Path.home() / ".hermes"; this PR uses the existing get_hermes_home() helper so HERMES_HOME overrides and platform-aware homes keep working (same direction as fix: replace hardcoded ~/.hermes fallbacks with platform-aware Windows paths #57216 / fix(profiles): replace hardcoded ~/.hermes paths with get_hermes_home() #26508).
• SVG badge names/tiers are XML-escaped so session-derived text can't inject markup into rendered sheets.

FastAPI response classes are stubbed in the existing no-FastAPI fallback so the plugin's dependency-free unit tests keep working.

Related Issue

Addresses the export/agent-summary section of #18472 (spec: #18151).

Type of Change

• ✨ New feature (non-breaking change that adds functionality)

Changes Made

• plugins/hermes-achievements/dashboard/plugin_api.py: add TIER_ORDER, agent_summary_path(), filter_and_sort_achievements(), export_json(), export_markdown(), export_svg(), _build_agent_summary(), _write_agent_summary(); new /export and /achievements/summary routes; write agent_summary.json in _run_scan_and_update_cache(); clear it in /reset-state; stub JSONResponse/PlainTextResponse in the FastAPI fallback.
• plugins/hermes-achievements/tests/test_export_and_summary.py: 13 new unit tests (state filtering, JSON structure/filter, Markdown header/categories/badges/bad-timestamp handling, SVG rows/escaping/empty sheet, agent summary strengths/gaps/top-tier/empty data, agent_summary.json persistence).
• plugins/hermes-achievements/README.md: document the new endpoints and the agent_summary.json artifact.

How to Test

1. cd plugins/hermes-achievements && python3 -m unittest discover -s tests -v — 21 tests (13 new + 8 existing engine tests) pass without dashboard dependencies.
2. Start the Hermes dashboard, open the Achievements tab once so a scan completes, then:
   • curl 'localhost:<port>/api/plugins/hermes-achievements/export?format=markdown' → Markdown badge table
   • curl 'localhost:<port>/api/plugins/hermes-achievements/export?format=svg' > badges.svg → renderable badge sheet
   • curl 'localhost:<port>/api/plugins/hermes-achievements/achievements/summary' → compact profile
3. Check $HERMES_HOME/plugins/hermes-achievements/agent_summary.json exists after the scan and disappears after POST /reset-state.

[frirenai]

Closing — reopening this from my main account.