ci: enforce the checks the contributor rules already required

Four gates that were documented but unenforced, plus the flaky test that
made a full-suite run untrustworthy.

Rust lint/format: CLAUDE.md has required `cargo fmt` and `cargo clippy`
before every commit for as long as the rule existed, yet neither ran
anywhere in CI — the requirement rested on memory alone. Both now run in
build-and-test.yml and build-release.yml. rustfmt and clippy are already
baked into the builder image, so nothing is installed at job time.
`cargo fmt --all -- --check` is strict immediately (the tree is clean).
Clippy is advisory for now: ~51 pre-existing warnings mean `-D warnings`
would fail on unrelated work, so the step carries a TODO to flip the flag
once the backlog clears. A compile error still fails it, so it is not a
no-op.

Traceability threshold: MIN_THRESHOLD sat at 50 while real coverage was
86%, so nearly half the matrix could rot before the gate objected.
Ratcheted to 82 with the policy written down — it only ever goes up, and
is never lowered to make a red build pass. The same figure lives in
MIN_COVERAGE_PERCENT so `traces:coverage` gates locally on the same bar,
and a test fails if the two drift.

Dangling IDs: a TRACES comment could name any well-formed ID and the
extractor accepted it silently, so typos and renames that missed a call
site passed unnoticed. `bun run traces:validate` cross-checks every
traced ID against the table rows in requirements.md and fails with the
referencing files listed. It spans UT/IT as well, which the coverage
orphan list ignores by design. This currently reports DR-189 and UT-188,
which are being defined separately.

Flaky offlineCatalog test: the first dynamic import of the service paid
~1s to transform its dependency graph, charged to a test body against
vitest's 5s default. Alone it passed; under suite-wide contention it
timed out. The import is now warmed at collection time, so no test is
timing the compiler — the timeout is deliberately unchanged. The store
shim also drops subscribers from module instances discarded by
resetModules, which previously leaked across tests.

package.json

@@ -39,6 +39,7 @@
     "traces:json": "bun run scripts/extract-traces.ts --format json",
     "traces:markdown": "bun run scripts/extract-traces.ts --format markdown > docs/traceability.md",
     "traces:coverage": "bun run scripts/extract-traces.ts --format coverage",
+    "traces:validate": "bun run scripts/extract-traces.ts --format validate",
     "release:notes": "bun run scripts/release-notes.ts"
   },
   "license": "MIT",