fix: ignore scanner metadata files

[floze-the-genius]

Summary

• exclude HISTORY.md, CHANGES.md, AUTHORS, NOTICE, .gitignore, and .gitkeep from scanner candidates
• use one case-insensitive predicate for top-level and nested flat Markdown scans
• add a Bun regression test and run it in CI
• rebuild the tracked Obsidian plugin bundle

Validation

• bun test — 1 passed
• bun run build
• bun run lint
• bun run scripts/check-tool-count.ts
• git diff --check

Closes #41

[vercel]

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