Convert skipHookPrefix to skipHookPrefixes (string to []string)

[slavshik]

Summary

• Converts git.skipHookPrefix (single string) to git.skipHookPrefixes (array of strings), allowing users to specify multiple prefixes that skip git hooks (e.g. ["WIP", "fixup!", "squash!", "amend!"])
• Adds a config migration from the old skipHookPrefix scalar to the new skipHookPrefixes sequence for backward compatibility
• Default value remains ["WIP"] preserving existing behavior

Closes #2275

Test plan

• make build — compiles successfully
• go test ./... -short — all unit tests pass
• make lint — no lint errors
• make generate — schema/docs regenerated
• New test cases for multiple prefixes in CommitCmdObj, CreateFixupCommit, CreateAmendCommit
• Migration test cases: old field only, new field only, both present, neither present

🤖 Generated with Claude Code