Add agent discoverability surfaces

[mikedotexe]

What this PR adds

Static metadata and tooling that lets AI agents and crawlers self-bootstrap to FastNear's surfaces, plus a generator and audit pipeline to keep it consistent.

• static/.well-known/agent-skills/{index.json + 4 SKILL.md} — agentskills.io v0.2.0 discovery directory (overview, surface-routing, auth, playbooks)
• static/.well-known/api-catalog — RFC 8615 linkset for RPC, FastNear API, and NEARData (with service-desc, service-doc, status per service)
• src/data/openapiSnapshots/{fastnear,neardata}.json (canonical, hand-vendored) → static/openapi/{fastnear,neardata}.json (build mirror via copyOpenApiSnapshots() in scripts/generate-ai-surfaces.js)
• static/_headers — advertises the discovery surfaces via HTTP Link headers (RFC 8615 / agent-skills) on every route
• static/_worker.js — serves .md mirrors via content negotiation (Accept: text/markdown) and adds the matching Link headers
• static/robots.txt — adds Cloudflare AI Content Signals: Content-Signal: search=yes, ai-input=yes, ai-train=yes
• scripts/generate-ai-surfaces.js — extended (~233 lines) to drive the artifacts above; SKILL.md files also pick up the existing "About FastNear" footer CTA
• scripts/audit-indexing-surface.js — extended (~509 lines) to validate the new static surface area; runs in ci:locale-quality post-build (no new CI gating beyond what's already there)
• scripts/audit-agent-readiness-live.js + audit:agent-readiness:live — manual live smoke test against the deployed origin, validates the Link headers and .md content negotiation are wired correctly

Hosting

docs.fastnear.com is on Cloudflare Pages (visible from the repo's Cloudflare Pages GitHub status check), so static/_headers and static/_worker.js are load-bearing — they execute on the edge once this merges. No infra change required.

Current branch status

Rebased onto current main (post #20 and #21 example-tightening merges). Two real fixes surfaced from the rebase + regen:

1. The four SKILL.md files now correctly include the "About FastNear" footer CTA that landed on main after this branch was first opened.
2. static/ru/** markdown caught up to main's tightened example content.

Verification

• yarn build clean (en + ru both compile)
• node scripts/audit-indexing-surface.js clean against local build (Indexing surface audit passed for 105 explicit docs routes, 78 docs operation pages, and 78 hosted operation pages.)
• yarn generate:ai-surfaces is idempotent: re-running produces no further drift
• OpenAPI build mirror is in sync with the canonical source (formatting differs — — escaping vs raw em-dash from JSON.stringify re-encoding — but semantically identical)
• Live audit script is manual-only: not present in ci:locale-quality or any other ci:*/audit:* aggregate
• Spot-checked: SKILL.md files end with the "About FastNear" footer block; robots.txt has the Content-Signal line

Test plan

• Rebase onto current main is clean
• yarn build exits 0 for both locales
• node scripts/audit-indexing-surface.js exits 0 against the local build tree
• Generator output is idempotent (second run produces no diff)
• Cloudflare Pages preview deploy succeeds
• Post-merge: SITE_ORIGIN=https://docs.fastnear.com node scripts/audit-agent-readiness-live.js exits clean (validates Link headers, .well-known/api-catalog, .well-known/agent-skills/index.json, and .md content negotiation are live)

Out of scope for this PR

• Wiring audit:agent-readiness:live into CI (kept manual until we trust the live signal across a few deploys)
• Auto-pulling upstream OpenAPI specs into src/data/openapiSnapshots/ (manual snapshot maintenance for now; document a sync cadence in a follow-up)

[cloudflare-workers-and-pages]

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Latest commit:	0fef871
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