File-size decomposition (no behavior change). Move the dependency-free encode/
decode helpers (sanitizeWatchHistoryMetadata, serializeWatchHistoryItems,
bytesToHex, looksLikeJsonStructure, hexToBytesCompat) into a new
js/nostr/watchHistoryCodec.js and import them back.
watchHistory.js: 2512 -> 2435 lines (back under its 2438 limit).
Build + full unit suite green.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
