chore(coverage): raise the agentsfleetd target to 92

Indy's call, reading the daemon's 90 against the 95 `runner` and `lib` carry.
It moves the published bar only: `breaches()` grades floors, so the daemon's
next two points now read as a printed gap on every graded run instead of a red
one. The enforced floor stays at 90 — the last Linux measurement was 90.21%,
and this file's raise-only rule moves a floor to what a run measured, never
ahead of it.

`docs/architecture/testing.md` carries the same pair; a parity test
(`check_zig_coverage_doc_test`) fails when the two disagree, so the table and
the prose move in this commit too.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>