v0.4.4: deleted-feature registry, retired bigram spec restored

v0.4.4: deleted-feature registry, retired bigram spec restored

Documentation only. The Go library is byte-identical to v0.4.3 -- no .go file
changed.

New since v0.4.3:

• specs/deleted.md (07557d5): a registry of capabilities microfts2
  deliberately does not have. A feature whose requirements are ALL retired has
  no live spec to cite, and pointing it at the spec that replaced it misstates
  what that spec covers -- api.md no longer describes Options.MaxDBs,
  storage.md no longer describes big-endian C records. Four features now cite
  deleted.md instead: Index Computation (R36), MaxDBs Option (R101/T56),
  Encoding (R123), Bigram Index (R379-R416, T17-T54).

  Each entry records what the feature was, when and why it went, and what
  replaced it, so an approach that was tried and rejected cannot be quietly
  re-proposed. The bigram entry carries the measured cost that killed it --
  2.5s on 74K chunks, 1.7x index size.

• specs/migrations/complete/002-bigram-index-removed.md (9f2f6a9): the bigram
  spec restored verbatim from c8d1a19^. The requirements had cited BIGRAM.md,
  a path never tracked in this repo; the real spec was specs/bigram.md,
  deleted with the feature. Its number is recording order, not landing order
  -- the removal (2026-03-22) predates 001-lmdb-to-bbolt (2026-06-12).

• gitignore CLAUDE.local.md (7e2d3aa).

phase spec OK, query unindexed-specs empty, full suite green. phase
requirements fails on one approved item only: A2, the deliberately
non-sequential numbering that is never renumbered.

Daneel of Claude Opus 5

Co-Authored-By: Claude Opus 5 noreply@anthropic.com