fix: stop ignored local files from churning vault history

[AksharP5]

What changed

A Git-ignored transcript made Arch and Mac overwrite the same skill hash every sync, producing hundreds of registry-only commits. Registry generation and validation now exclude untracked files ignored by Git. Fixes #67.

Why

The previous hash included local files that Git never sent to other devices. Git supplies the ignored paths once per registry build or validation; tracked files remain included even when an ignore rule matches.

Safety and compatibility

• Existing vault migration: the next sync corrects affected hashes once, with no schema change.
• Local-file behavior: ignored files stay in place; copy overwrite protection still checks all deployed files.
• Destructive behavior: no file removal or history rewrite.
• Cross-device behavior: upgrade devices to prevent older versions restoring local-only hashes.

Validation

• npm test: 112 tests pass, including two-clone hash stability, tracked ignored files, deletion, repeated imports, and copy drift protection.
• npm pack --dry-run
• git diff --check
• Patched hashing on the actual Arch skill matches the Mac's hash. macOS/Linux CI runs on this PR.