Replace native Git with Dugite to support users without Git installed (#1760)

I moved all isomorphic-git usage into a single git_utils.ts file and
added Dugite as an alternative Git provider. The app now checks the
user’s settings and uses dugite when user enabled native git for all
isomorphic-git commands. This makes it easy to fully remove
isomorphic-git in the future by updating only git_utils.ts.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds Dugite-based native Git (bundled binary) and refactors all Git
calls to a unified git_utils API, replacing direct isomorphic-git usage
across the app.
> 
> - **Git Platform Abstraction**:
> - Introduces `dugite` and bundles Git via Electron Forge
(`extraResource`) with `LOCAL_GIT_DIRECTORY` setup in `src/main.ts`.
> - Adds `src/ipc/git_types.ts` and a comprehensive
`src/ipc/utils/git_utils.ts` wrapper supporting both Dugite (native) and
`isomorphic-git` (fallback): `commit`, `add`/`addAll`, `remove`, `init`,
`clone`, `push`, `setRemoteUrl`, `currentBranch`, `listBranches`,
`renameBranch`, `log`, `isIgnored`, `getCurrentCommitHash`,
`getGitUncommittedFiles`, `getFileAtCommit`, `checkout`,
`stageToRevert`.
> - **Refactors (switch to git_utils)**:
> - Replaces direct `isomorphic-git` imports in handlers and processors:
`app_handlers`, `chat_handlers`, `createFromTemplate`,
`github_handlers`, `import_handlers`, `portal_handlers`,
`version_handlers`, `response_processor`, `neon_timestamp_utils`,
`utils/codebase`.
> - Updates tests to mock `git_utils`
(`src/__tests__/chat_stream_handlers.test.ts`).
> - **Behavioral/Feature Updates**:
> - `createFromTemplate` uses `fetch` for GitHub API and `gitClone` for
cloning with cache validation.
> - GitHub integration uses `gitSetRemoteUrl`/`gitPush`/`gitClone`,
handling public vs token URLs and directory creation when native Git is
disabled.
> - Versioning, imports, app file edits, migrations now stage/commit via
`git_utils`.
> - **UI/Copy**:
>   - Updates Settings description for “Enable Native Git”.
> - **Config/Version**:
>   - Bumps version to `0.29.0-beta.1`; adds `dugite` dependency.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
ba098f7f25d85fc6330a41dc718fbfd43fff2d6c. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Will Chen <willchen90@gmail.com>

package.json

@@ -135,6 +135,7 @@
     "date-fns": "^4.1.0",
     "dotenv": "^16.4.7",
     "drizzle-orm": "^0.41.0",
+    "dugite": "^3.0.0",
     "electron-log": "^5.3.3",
     "electron-playwright-helpers": "^1.7.1",
     "electron-squirrel-startup": "^1.0.1",