docs: add commit conventions skill

.agents/skills/commit-conventions/SKILL.md

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+---
+name: commit-conventions
+description: How to write git commits for this repository. Use when committing changes, writing commit messages, or splitting work into commits. Covers conventional commit format and separating commits by concern.
+---
+
+# Commit Conventions
+
+Follow these rules whenever you create a commit in this repository.
+
+## Conventional Commits
+
+Write every commit message using the [Conventional Commits](https://www.conventionalcommits.org/) format:
+
+```
+<type>(<scope>): <subject>
+```
+
+- **type**: `feat`, `fix`, `chore`, `docs`, `refactor`, `perf`, `test`, `build`, `ci`, `style`.
+- **scope** (optional): the area of the codebase the change touches. Use the workspace package or directory name when it's clear (e.g. `proxy`, `web`, `packages`). Omit when the change spans multiple areas.
+- **subject**: imperative mood, capitalized, no trailing period, ≤ 50 characters.
+
+Examples:
+
+```
+feat(proxy): add TTS streaming endpoint
+fix(web): handle empty transcript in player
+docs: document workspace layout
+```
+
+## Separate Commits by Concern
+
+Do not bundle unrelated changes into a single commit. Split work so each commit is a focused, self-contained unit:
+
+- One logical change per commit (a feature, a fix, a refactor, a doc update).
+- Keep each commit buildable and independently reviewable.
+- Separate concerns that have different types, scopes, or reasons to be reverted independently.
+- If a change is large, split it into a series of smaller commits that each stand on their own.
+
+## Message Body
+
+Include a body only when it adds useful context beyond the subject. If the subject fully captures the change, omit it.
+
+- Separate the subject from the body with a blank line.
+- Wrap the body at 72 characters.
+- Explain the *why* and *what* rather than restating the code.
+- Do not repeat information already in the subject line.
+- Use `BREAKING CHANGE:` in the body (or `!` after the type/scope) for breaking changes.
+
+## When to Use This Skill
+
+Activate this skill when:
+
+- Creating a new commit.
+- Writing or revising a commit message.
+- Deciding how to split staged or unstaged changes into commits.