linux: drop macos dialog message and allow creating folders

[thedhruvhegde]

summary

electron on linux does not support message on showOpenDialog, so the directory picker could fail or look broken. createDirectory was also false, so you could not make a new folder from the picker.

message stays on darwin. linux/win get createDirectory: true without that option.

closes #2336

test plan

• linux: add workspace / pick directory and confirm the dialog opens
• linux: create a folder from the picker
• macos: still shows the extra message on the directory dialog

[greptile-apps]

Greptile Summary

This PR makes native open-dialog options platform-specific for directory and audio-file selection.

• Retains caller-provided dialog messages on macOS while omitting the unsupported option elsewhere.
• Attempts to enable directory creation on Linux and Windows, but applies a macOS-only Electron option to those platforms.

Confidence Score: 4/5

The PR should not merge until the directory-creation implementation is corrected because the targeted Linux workflow remains unfixed.

The message handling matches Electron's platform contract, but the new createDirectory branch is inverted relative to that contract and therefore cannot deliver the stated behavior.

Files Needing Attention: apps/emdash-desktop/src/main/core/app/service.ts

Important Files Changed

Filename	Overview
apps/emdash-desktop/src/main/core/app/service.ts	Introduces platform-specific dialog options, with createDirectory guarded for the platforms where Electron does not support it.

Prompt To Fix All With AI

### Issue 1
apps/emdash-desktop/src/main/core/app/service.ts:609-612
**Unsupported folder creation option**

Electron's `createDirectory` option is macOS-only, but this branch adds it only on Linux and Windows, where it is ignored, and omits it on macOS, where it is supported. As a result, the directory picker still cannot create folders in the targeted Linux flow, so the reported bug remains unresolved.

---

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

_{Reviews (1): Last reviewed commit: "stop passing macos-only dialog message o..." | Re-trigger Greptile}

[greptile-apps]

Unsupported folder creation option

Electron's createDirectory option is macOS-only, but this branch adds it only on Linux and Windows, where it is ignored, and omits it on macOS, where it is supported. As a result, the directory picker still cannot create folders in the targeted Linux flow, so the reported bug remains unresolved.

Prompt To Fix With AI

This is a comment left during a code review.
Path: apps/emdash-desktop/src/main/core/app/service.ts
Line: 609-612

Comment:
**Unsupported folder creation option**

Electron's `createDirectory` option is macOS-only, but this branch adds it only on Linux and Windows, where it is ignored, and omits it on macOS, where it is supported. As a result, the directory picker still cannot create folders in the targeted Linux flow, so the reported bug remains unresolved.

---

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