feat(source-control): complete git panel workflow

[viniraioli]

What

Completes the Git source control workflow with a polished source-control panel, status count badge, staged/unstaged groups, discard actions, commit/push affordances, and AI-generated Conventional Commit messages for staged changes.

This continues the inactive draft work in #174 and turns the source-control surface into a usable review/stage/commit flow.

Why

Closes #194
Closes #243
Closes #87
Refs #1

Terax users need a first-class Git workflow for reviewing AI-generated changes without leaving the app or falling back to another editor. The existing draft PR #174 already established the direction; this PR picks up that work and fills in the missing workflow polish.

How

• Adds the registered git_discard command and backend discard support for tracked and untracked files.
• Refines the Source Control panel with compact layout behavior, file icons, status codes, safer disabled states, confirmation-backed discard controls, and persistent panel sizing.
• Exposes a header badge with the current changed-file count.
• Reuses the configured AI model path to generate valid Conventional Commit subjects from staged diffs.
• Keeps push disabled until an upstream exists, with a clear hint instead of a silent no-op.

Testing

• pnpm exec tsc --noEmit clean
• Manual smoke-test of the affected feature
• (If you touched src-tauri/) cargo check clean
• (If UI) tested in pnpm tauri dev

Screenshots / GIFs

Source Control staged list	Commit footer

Notes for reviewer

Related PR: #174 is the existing draft source-control implementation this follows up on.

[viniraioli]

@crynta Hi, do you have an estimated timeline for implementing this control panel feature? Version control support is really important for day-to-day use in Terax, so I wanted to check whether this is likely to land soon or if it is still expected to take a bit more time. Thanks.

[crynta]

@viniraioli Hi, thanks for asking, I’m actually looking at this right now and gonna merge it soon. It was originally supposed to be included in 0.6.6, but there were a couple of pretty obvious terminal issues I wanted to fix first, especially after the BetterStack video (btw, thanks to them for that :) ). So I decided to quickly fix those, ship the release, and then move on to new features like source control, the new AI agents workflow, improved web preview, extensions, etc. with source control being the first priority