Add observability to import-boundary CLI (verbose flag, scan summary, unresolved-import diagnostics)

[coderabbitai]

Background

PR #3 introduced scripts/lint-import-boundaries.ts as the CLI wrapper for import-boundary enforcement. The checker currently produces output only when violations are found and provides no operation-context logging, scan statistics, or visibility into unresolved imports.

Requested work

Extend the CLI to support maintainer observability:

1. Scan start/end logging — emit a structured message when scanning begins and completes (file count, duration).
2. Summary statistics — report total files scanned, violations found, and unresolved imports encountered.
3. --verbose flag — when passed, emit per-file resolution detail and unresolved-import diagnostics to stderr.
4. Unresolved-import diagnostics — when an import specifier cannot be resolved to a known source file, emit a diagnostic (currently silent).

All new output must be written to stderr only and must not affect the exit-code contract (0 = clean, 1 = violations).

Acceptance criteria

• bun run lint:imports --verbose emits scan context and per-file details.
• Unresolved imports are surfaced as warnings, not errors.
• Existing main() dependency-injection interface (LintImportBoundaryDependencies) is preserved and extended where necessary.
• Tests cover the new output paths.

References

• PR: Record source-tree boundary decision (1.1.2) #3
• Requester: @leynos