#14904: fix(nostr): handle string return from nip19.decode in normalizePubkey

## Summary - Fixes #8570 - `nostr-tools` ≥2.23 changed `nip19.decode()` to return a hex string for `npub` keys instead of `Uint8Array` - `normalizePubkey()` used `Array.from(decoded.data)` which splits a string into individual characters, producing garbage hex output (128 chars of per-byte hex instead of 64) - Added a `typeof` check before the `Uint8Array` conversion to handle both string (≥2.23) and `Uint8Array` (older) return types ## Test plan - [x] Added 2 new tests for `normalizePubkey` npub format handling (converts npub to hex, roundtrips with `pubkeyToNpub`) - [x] Added 2 new tests for `validatePrivateKey` nsec format (accepts valid nsec, returns same bytes as hex equivalent) - [x] Fixed pre-existing invalid `TEST_NSEC` constant (bad checksum) by dynamically encoding from `TEST_HEX_KEY` - [x] All 4 new tests fail before the fix, pass after - [x] All 36 tests pass 🤖 Generated with [Claude Code](https://claude.com/claude-code) <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates the Nostr extension’s `normalizePubkey()` helper to correctly handle `nostr-tools`’ `nip19.decode()` behavior change for `npub` keys (returning a hex `string` instead of a `Uint8Array`), preventing incorrect hex normalization. It also adds test coverage for: - `normalizePubkey` npub handling (npub → 64-char lowercase hex, roundtrip with `pubkeyToNpub`) - `validatePrivateKey` nsec handling (accepts a valid nsec, returns expected bytes) No merge-blocking issues were found in the changeset. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - The change is narrowly scoped (type guard on `decoded.data`), preserves previous behavior for older `nostr-tools` versions, and is covered by targeted new tests for both npub and nsec flows. No regressions or incorrect assumptions were identified within the repository code. - No files require special attention _{Last reviewed commit: d8dd20e} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->