[TheGreatAxios]

Replaces copies of helpers that already exist with the shared version, with no change in behaviour, across four commits. The shared helpers errorText, isRecord, optionalString, decodedSegment and counted now live in @corbits/common; githubAppLogin and mirrorCallId are reused where they were copied; the extension has one settle.

• errorText replaces the inline instanceof Error ternary everywhere it was written out, including the eval fixtures, the model test and the check pack. repo-read-tool and tests/model now depend on @corbits/common (workspace:*).
• counted moved from the portal into @corbits/common and replaces every other pluraliser (portal pages, the triage comment, the review-clean findings text). apps/web/src/lib/plural.ts is gone. The portal's triage-view.ts counted formats numbers differently and stays.
• The tenant PATCH route and the workflow-release triggers use decodedSegment; two hub tests build the mirror id with mirrorCallId.

Verified with bun run check, bun run lint (only existing warnings), bun run test:unit and the manager-routes and server Postgres tests, run three times.

Closes CL-11777

[linear-code]

CL-11777

[corbits-triage]

Triage: Pass

No changes needed from you. A maintainer will review this pull request.

Notes:

• pull request is over the files limit: 38 files (max 30)
• changes sensitive paths: locks: bun.lock
• Risk: medium (locks paths, 38 files, 18 recently fixed files)

[corbits-triage]

Replaces duplicated helpers across the monorepo with shared versions from @corbits/common (errorText, isRecord, optionalString, decodedSegment, counted), reuses githubAppLogin and mirrorCallId where they were copied, and consolidates the extension's settle into one module. The change is intended to be behaviour-preserving, and the description reports passing checks, lint, and tests.