epic: in-app git workflow actions

[chuks-qua]

Description

Developers using mcode complete agent-driven coding tasks in worktrees but must leave the app to push branches, create pull requests, and check CI status. This forces context-switching to the terminal and GitHub web UI for the final steps of every workflow. This epic closes that gap by adding push, PR creation, and CI visibility directly in the app.

Scope

In Scope

• Push branches to remote from the UI
• Create GitHub pull requests with AI-generated titles and descriptions
• View GitHub Actions check status on threads and PRs
• Manual commit creation from the UI (stage, message, commit)

Non-Goals

• PR review or commenting (reading or submitting GitHub reviews in-app)
• PR merge or close operations
• Git rebase, stash, or conflict resolution UI
• GitHub Actions workflow triggering or re-running
• Commit amend or interactive rebase

Success Metrics

• Users can go from "agent finished work" to "PR created" without leaving mcode
• CI pass/fail status is visible on every thread with a linked PR
• Manual commits can be created for ad-hoc edits outside agent work

Background

T3 Code ships PR creation with AI-generated titles/bodies and a stacked commit+push+PR flow. Mcode already has the read side (PR badges, commit viewer, branch picker with PR tab) but lacks all write operations and CI visibility. The gh CLI is already a dependency for existing GithubService methods, so extending it is low-risk.

Affected Areas

• Server git and GitHub services
• WebSocket RPC methods and contracts
• Chat header and diff toolbar UI components
• Thread model (CI status fields)

Acceptance Criteria

• A user can push a branch and create a PR from the chat header without leaving the app
• PR title and body are pre-filled using AI summarization of the branch diff
• GitHub Actions check status appears on threads with linked PRs
• A user can stage files, write a commit message, and create a commit from the UI

Feature Breakdown

Stream A:  [feat 1: PR creation]

Stream B:  [feat 2: CI status]

Stream C:  [feat 3: Commit UI]

Critical path: feat 3 (8 pts)
Max parallelism: 3 streams