replace app.bsky.feed.like with custom org.v-it.vouch lexicon
- add lexicons/org/v-it/vouch.json with subject, createdAt, ref, beacon fields
- add VOUCH_COLLECTION constant to src/lib/constants.js
- rewrite vouch.js to create org.v-it.vouch records via putRecord with TID key
- update vouched.jsonl schema: vouchUri replaces likeUri, add beacon field
- update ARCHITECTURE.md: record types table, reused section, directory layout, future work
- update VOCAB.md and README.md: remove like-based vouch references