Allow importing EML files into any mailbox folder (not just INBOX)

[Copilot]

PUT /api/Messages hardcoded the destination folder to INBOX. This adds an optional folderName query parameter so callers can import into any folder (e.g. Sent), defaulting to INBOX for backward compatibility.

Changes

• MessagesController.cs — Added optional folderName parameter (default: MailboxFolder.INBOX) to ImportMessage; folder lookup now uses it instead of the hardcoded constant
• ApiClient/MessagesController.ts — import_url and import accept an optional folderName (default: "INBOX") appended as a query parameter
• messagelist.vue — Import call now passes selectedFolder so files are imported into whichever folder the user is currently viewing

API

PUT /api/Messages?mailboxName=Default&folderName=Sent
Content-Type: message/rfc822

<eml content>

[sonarqubecloud]

Quality Gate failed

Failed conditions
B Reliability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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[rnwood]

@copilot in the UI when uploading, upload to the currently selected folder

[Copilot]

@copilot in the UI when uploading, upload to the currently selected folder

This was already included in the previous commit (24dfe56) — messagelist.vue line 399 passes this.selectedFolder to the import call, so EML files are imported into whichever folder is currently selected in the UI.