Migration notes for akm v0.9.14

The derived `index.db` generation changes from v22 to v23 to support lexical
Markdown fragments. On the first normal read after upgrade, akm detects that
the v22 cache cannot serve queries and performs one inline v23 rebuild from
currently materialized sources before serving the request. An explicit
`akm index` performs the same writable rebuild. No hand-written database
migration or manual deletion is needed, but the first rebuild may take longer
than a normal read. Do not run an older akm against an index this release has
already rebuilt: upgrade that binary instead. If v23 schema creation is
interrupted, the partial cache is not admitted as current; the next writable
open rebuilds it, while an existing/read-only opener reports that `akm index`
is required.

Search may now return an addressable `#akm-fragment-…` suffix for the matching
part of a long Markdown asset. Pass that returned ref to `akm show` to display
the exact indexed fragment.

If you use collapse-detector canaries, their baseline predates the new index
generation. After the `akm index` rebuild/reindex completes, explicitly mint a
new set from the repository checkout:

    bun scripts/refresh-canary-set.ts --refresh

The refresh is deliberate and is never automatic, so historical canary cycles
remain interpretable against their original baseline.