docs: align api.md and bring test client up to current feature set

[nedpals]

Summary

Follow-up to the README refresh (already merged). This PR brings the API reference and the browser test client in line with the agent's current feature set. No protocol or server code changes — documentation and the demo client only.

docs/api.md

• Fix the intro wording: the agent runs a multi-server architecture (Device / Client / CA Bootstrap), not "two-server" as the text said while the table listed three.

client/test-client.html

Previously the demo only knew about basic text/uri reads and writes. It now exercises the shipped capabilities:

• Tag capabilities displayed per scan (family, memory size, max NDEF size, writable/lockable, read-only state, password support) — read from the capabilities object already present on every tagData broadcast.
• Write verification results surfaced (tag type/UID, bytes written, verified, attempts, locked) — the writeResponse payload was previously discarded.
• Expanded write record types: mailto, tel, sms, geo, smartposter, mime, vcard, aar — with type-specific Title and MIME-type inputs.
• Lock after write option (sends lock: true) and an Erase Tag action (writes an empty record).

Backwards compatibility

All changes are backwards compatible:

• The documented protocol features were introduced additively (new optional fields on existing messages, new opt-in message types) — older clients keep working.
• The test client degrades gracefully against an older agent: the capabilities and verification panels are guarded with v-if and hide themselves when the data is absent; unsupported record types / lock / erase surface as a normal caught error rather than breaking the UI.

Testing

• Verified the documented message types and record types against server/constants.go and server/handlers.go.
• Confirmed the capability field names match nfc/capabilities.go and that NFCClient.write() resolves with the response payload (top-level uid/tagType/verified/etc.).

🤖 Generated with Claude Code

---

Generated by Claude Code