CI: cleanup and fix broken job references

- Fix code-size -> code-analysis job name (5 jobs had wrong dependency)
- Remove useless install-check job (was no-op)
- Add explicit docs_only guard to release-check
- Remove dead submodule checkout steps (no submodules in repo)
- Rename detect-docs-only -> detect-docs-changes, add docs_changed output
- Reorder check script: format first for faster fail
- Fix billing error test (PR #12946 removed fallback detection but not test)

src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts

@@ -17,7 +17,6 @@ describe("isBillingErrorMessage", () => {
       "Payment Required",
       "HTTP 402 Payment Required",
       "plans & billing",
-      "billing: please upgrade your plan",
     ];
     for (const sample of samples) {
       expect(isBillingErrorMessage(sample)).toBe(true);