Refine ExtractIssuePrefix to better distinguish hash IDs from English
words in multi-part issue IDs. Hash suffixes now require digits or be
exactly 3 chars, preventing "test", "gate", "part" from being treated
as hashes. This fixes prefix extraction for IDs like "vc-baseline-test".
Also updates git hooks to use -q flag and adds AGENTS.md documentation.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>