feat: display styled output after successful commit

[lb1192176991-lab]

What

After a successful commit, users now see a styled success message showing the abbreviated commit hash and first line of the commit message, instead of raw git output.

Why

Raw git commit output is noisy and inconsistent. A styled summary (green checkmark + bold hash + dimmed summary) provides immediate feedback that's consistent with the rest of commit-echo's UX.

Changes

• commit() in src/git/diff.ts now returns a CommitResult object with parsed hash and summary fields
• Auto-commit flow shows styled output with pc.green() and pc.dim()
• Manual commit flow also shows styled output
• Falls back to raw output if parsing fails

Testing

• npm run build passes
• Styled output shown in both auto-commit and manual-commit flows
• Error output still shown on failure (unchanged)

[404-Page-Found]

Please address the detached HEAD regex issue and extract the duplicated styled output block before merging. Both are straightforward fixes.

[404-Page-Found]

The regex \S+ only matches a single word for the branch ref. In detached HEAD state, git commit outputs [detached HEAD abc1234] — \S+ captures only detached, leaving HEAD unmatched by [a-f0-9]+. This causes the regex to fail, falling back to raw output.

Fix: Use [\w-]+(?:\s+[\w-]+)? or similar to capture multi-word refs like detached HEAD. Alternatively, use a more robust approach: match the hash after the last ] bracket, or use git rev-parse HEAD to get the hash directly instead of parsing the output string.

[404-Page-Found]

This styled output block is duplicated with the one in the manual-commit path below. Please extract it into a helper function like printCommitResult(result: CommitResult) to keep the code DRY.