Implements Timmy's Nostr identity stack in `src/infrastructure/nostr/`:
- **keypair.py**: Pure-Python secp256k1 keypair generation (BIP-340),
bech32 nsec/npub encoding (NIP-19), `generate_keypair()` / `load_keypair()`.
- **event.py**: NIP-01 event construction with BIP-340 Schnorr signing,
`build_event()` + `schnorr_sign()` / `schnorr_verify()`.
- **relay.py**: WebSocket relay client via `websockets`, publishes NIP-01
`["EVENT", …]` messages to one or many relays concurrently with graceful
degradation when unavailable.
- **identity.py**: `NostrIdentityManager` — publishes Kind 0 (profile
metadata) and Kind 31990 (NIP-89/NIP-90 capability card) to configured
relays; reads all settings from `config.settings`.
Config additions to `src/config.py`:
`NOSTR_PRIVKEY`, `NOSTR_PUBKEY`, `NOSTR_RELAYS`, `NOSTR_NIP05`,
`NOSTR_PROFILE_NAME`, `NOSTR_PROFILE_ABOUT`, `NOSTR_PROFILE_PICTURE`.
All operations degrade gracefully (log WARNING, never crash) when keys or
relays are not configured — consistent with the project's error-handling
patterns.
Tests: 647 unit tests pass; new tests cover keypair, event signing/verify,
and the full identity announce lifecycle.
Fixes#856
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
