feat: add commit message generator skill for concise message suggestions

.factory/skills/commit_message/SKILL.md

@@ -0,0 +1,62 @@
+---
+name: commit_message
+description: Generate a concise one-liner commit message by analyzing staged changes and recent git history. Use when the user wants a commit message suggestion before committing.
+user-invokable: true
+disable-model-invocation: false
+---
+
+# Commit Message Generator
+
+## Overview
+
+Generate a concise, meaningful one-liner commit message by inspecting the staged diff and recent commit history. Sometimes staged files relate to a prior commit, so the previous commit is also reviewed for context.
+
+## Workflow
+
+### Step 1: Gather Context
+
+Run these commands to collect the necessary information:
+
+```bash
+# Get the last commit message and diff for context
+git log -1 --format="%h %s" && echo "---" && git diff HEAD~1 --stat
+
+# Get the staged diff (what will be committed)
+git diff --staged
+```
+
+### Step 2: Analyze the Changes
+
+- Read the staged diff to understand **what** changed.
+- Read the last commit (`git log -1`) to understand if the staged changes are a continuation, fix, or follow-up to the previous commit.
+- If staged files overlap with files in the last commit, treat the changes as related and reflect that in the message.
+
+### Step 3: Generate the Message
+
+Compose a **single-line** commit message following these rules:
+
+- **Format:** `<type>: <concise description>`
+- **Types:** `feat`, `fix`, `refactor`, `docs`, `style`, `test`, `chore`, `perf`, `ci`, `build`
+- **Length:** Under 72 characters
+- **Tone:** Imperative mood ("add", "fix", "update", not "added", "fixed", "updated")
+- **No period** at the end
+
+### Step 4: Output
+
+Print only the suggested commit message — nothing else. No explanation, no alternatives.
+
+## Examples
+
+```
+feat: add retry logic to API client
+fix: correct off-by-one error in pagination
+refactor: extract auth middleware into separate module
+docs: update README with new installation steps
+chore: bump dependencies to latest versions
+```
+
+## Tips
+
+- If the staged diff is empty, inform the user: "No staged changes found. Stage files with `git add` first."
+- If the staged changes clearly extend the previous commit (same files, same feature), phrase the message as a continuation rather than a new change.
+- Keep it specific — avoid vague messages like "update code" or "fix stuff".