fix(fullsend): add yarn fix, build:api-reports, and dedupe to workspace routing skill (#3520)

The monorepo-workspace-routing skill only ran yarn install but did not
execute Backstage maintenance commands, causing code agent PRs to fail
three CI gates: yarn fix --check, yarn build:api-reports, and lockfile
duplicate verification. Add Step 5 to run all three commands after
dependency installation so generated artifacts are committed.

Closes #3517

Co-authored-by: fullsend-code <278716306+fullsend-ai-coder[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: fullsend-ai-coder[bot]