feat(cli): comprehensive indexer logging

[prosdev]

Summary

Add comprehensive logging to all indexers (code scanner, git history, GitHub issues) for better visibility during indexing operations.

Changes

Code Scanner & Indexer

• Add logger option to ScanOptions and IndexOptions
• Log per-language file counts during discovery
• Log scan progress per language (start/complete)
• Log embedding progress every 10 batches
• Spinner shows: Embedding 4480/49151 documents (9%)

Git Indexer

• Add logger option to GitIndexOptions
• Log commit extraction count
• Log embedding progress every 10 batches
• dev git index --verbose for debug output
• Spinner shows: Embedding 320/500 commits (64%)

GitHub Indexer

• Add logger and onProgress to GitHubIndexOptions
• Log document fetch count and type breakdown
• dev gh index --verbose for debug output
• Spinner shows: Embedding 50/150 GitHub docs

Go-Specific Exclusions

• *.pb.go (protobuf), *.gen.go (generators)
• mock_*.go, mocks/, testdata/

Example Output

[scanner] Starting repository scan {repoRoot: "."}
[scanner] Found 4338 go files {language: "go", files: 4338}
⠧ Embedding 4480/49151 documents (9%)

[git-indexer] Extracted commits {commits: 500}
⠧ Embedding 320/500 commits (64%)

[github-indexer] Fetched GitHub documents {documents: 150}
[github-indexer] Document breakdown {issues: 100, prs: 50}
⠧ Embedding 50/150 GitHub docs

Testing

• 1552 tests passing
• Tested on large Go codebase (~4k Go files, 49k documents)