fix(admin): let the add-app dialog accept a typed branch

[mihir-kandoi]

Stacked on #377.

The add-app dialog's manual-URL branch picker passes allowCustomValue, which doesn't exist in frappe-ui 1.0.0-beta.34 — it lands on the <input> as an inert DOM attribute, so the promised "Type one to use it" flow silently never commits. This extracts #377's pick-or-type options into a shared branchComboboxOptions helper, points both the wizard and the dialog at it, and switches the dialog's manual picker to the same button-trigger custom-row pattern. The connected-GitHub picker stays list-only, as before.

Typed branches still go through resolveApp, so an invalid name can't be submitted. Unit tests cover the helper via the existing node --test harness; npm run build passes.

[tanmoysrt]

@greptile review

[greptile-apps]

Confidence Score: 4/5

The PR appears safe to merge, with the non-blocking request to cover the dialog’s typed-branch interaction.

The implementation mirrors an existing branch-picker pattern, but helper-only tests do not protect the newly changed component wiring.

Files Needing Attention: admin/frontend/dashboard/src/components/apps/AddAppFromGithubDialog.vue

Prompt To Fix All With AI

### Issue 1
admin/frontend/dashboard/src/components/apps/AddAppFromGithubDialog.vue:216
**Untested dialog integration**

Add a regression test that exercises typing and selecting a custom branch through this dialog; the existing helper-only tests do not cover the changed `trigger`, slot, and `v-model` integration, so that user flow can regress while the tests remain green.

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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

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