Fix existing Biome lint debt blocking documentation-only PRs

[shtse8]

Problem

Documentation-only project manifest PR #70 is blocked by the existing CI lint gate.

Failed run evidence:

• https://github.com/SylphxAI/bump/actions/runs/27913395878
• job test, step Lint
• command: bun run lint -> biome check .
• terminal summary: Found 24 errors. Found 4 warnings.

Representative diagnostics include import ordering, formatting, unused imports/variables, non-null assertions, and template-literal style issues in source/test files such as src/cli.ts, src/commands/add.ts, src/commands/pr.ts, src/commands/publish.ts, src/core/bumpfile.ts, and tests/release.test.ts.

Scope

This is not caused by the new PROJECT.md, .doctrine/project.json, or AGENTS.md files. Do not bypass branch protection. Fix the existing Biome diagnostics or intentionally adjust the lint policy so documentation-only PRs can pass through normal CI.

Acceptance

• bun run lint passes on the default branch.
• Re-run or refresh PR docs: add project manifest #70 and confirm the CI test job passes.
• Keep broad source formatting/lint cleanup separate from the project-manifest rollout unless explicitly approved.