v1.5.0

v1.5.0: discovered posts library — automatic caching + inspire command

Every search, timeline, read, mentions, and engage feed now caches external
posts into a local discovered_posts SQLite table. Zero extra API calls —
just stops discarding data we already fetch.

New features:
- discovered_posts table with UPSERT semantics (re-encounters update metrics,
  preserve first_source/discovered_at, backfill media URLs from read)
- Cache taps in 6 commands: search, timeline, mentions, read, engage recommend,
  engage feed
- New `xmaster inspire` command to query the library:
  --topic, --author, --min-likes filters, sorted by impressions
- query_discovered_posts() and discovered_posts_count() store methods

The library builds itself from normal usage. Over time it becomes a personal
collection of high-performing posts from the user's niche — like SuperX's
10M viral library, but personal, always fresh, and fully local.