docs: complete public API endpoint index with curl examples

[liu971227-sys]

Summary\n- expand docs/API.md into a complete public endpoint index\n- add curl examples for read/write endpoints, including signed and admin-protected routes\n- keep links to PROTOCOL.md, GLOSSARY.md, okenomics_v1.md, and OpenAPI spec\n- update docs/README.md quick links to include OpenAPI schema and the expanded API reference\n\n## Why\nThis addresses bounty #8 acceptance criteria around API documentation coverage and runnable examples for developers and agents.\n\n## Notes\n- docs-only change\n- no runtime code changes\n- examples use -k because the node may present a self-signed TLS certificate\n

[Scottcjn]

Closing for now: docs rewrite introduces encoding/format regressions and overlaps with existing API docs work.

Please keep participating. To be payout-eligible on resubmission:

1. Map directly to an active bounty issue and claim in that thread
2. Submit focused, non-duplicate changes
3. Include working proof (logs/screenshots/test notes)
4. Keep PR merge-ready (clean diff, no encoding regressions, no placeholder code)

Good active options right now: #99 (challenge), #100 (discovery), #102 (capability), #103 (social), #124 (profile micro-bounty).