docs: correct the migration count from 171 to 172 (unblocks Docs Gates)

[anhtahaylove]

check:docs-counts compares documented counts against the real file count in src/lib/db/migrations, which currently holds 172 .sql files. Three docs still say 171, which the checker treats a...[truncated]

[anhtahaylove]

Verified locally: this PR alone still shows Docs Gates red, because it inherits the malformed changelog.d/fixes/13094-*.md fragment from the base branch (that is the Merge integrity gate, fixed by #13158).

Applying both #13158 and #13160 on top of a clean release/v3.8.51:

• npm run check:changelog-integrity → 0 violations
• npm run check:docs-counts → exit 0, no STRICT drift (2 pre-existing soft warnings remain, non-blocking)

So the two together clear both base-red gates for every open PR; neither is sufficient on its own.

[anhtahaylove]

Context for the wider queue: this PR and #13158 are the two base fixes that unblock the other twelve leak PRs — full ordered list and CI triage in this comment.

The Unit Tests fast-path red on this PR is worth a glance precisely because this PR is docs-only: it changes 171 to 172 in three markdown files and cannot touch runtime behaviour, yet the unit-test job still fails — with a different set of tests than the other PRs fail. That asymmetry is the clearest evidence the unit-test flakiness is pre-existing on release/v3.8.51.

[anhtahaylove]

Closing as obsolete — already fixed on base.

release/v3.8.51 has moved 36 commits since this was opened, and the migration count is now correct upstream:

$ git show origin/release/v3.8.51:README.md | grep -oE "17[0-9] migrations"
172 migrations

Gate verified directly on current base:

$ npm run -s check:docs-counts
✓ All checks pass.
EXIT=0

Together with #13158 (closed for the same reason), the two base-red gates that were blocking the queue are green without either PR. All 15 remaining PRs report MERGEABLE.