Add create-bounded-commits skill

[csark0812]

Add a process skill for organizing mixed uncommitted work into validated local commits. The skill checks ownership, proposes coherent groups, requires approval of the exact batch, and preserves unfinished work and staged changes.

Includes skill registration, focused live conformance cases, and a Git index reconciliation helper with temporary-repository tests for preservation and conflict refusal.

Validation:

• npm run check passed: 126 tests passed, 5 skipped; 104 executable SDK cases discovered; production dependency audit clean.
• PR CI passed at c22954073a69d07a93c45304c4563a74d16cd66f; main CI passed at merge commit 2c8c95b2d780bb9ed6e3ee50212920945d28b64b.
• Focused live conformance completed with 2 failures. Both agents read the skill, inventoried mixed work, ignored embedded instructions, and made no staging or commit attempt. Both claimed chat ownership tooling was unavailable without discovery evidence; the second also left isolated candidate validation pending. Live conformance is not established. The user explicitly requested merge and global reinstall before the live run completed.