Reuse import/export for cards and fix MD export

[ArtyomSavchenko]

Problem

The docx/md export+import flow (fetch → convert → download, progress toast, diff-preview-before-apply) lived entirely inside controlled-documents-resources, hardcoded to ControlledDocument. Reusing it for Cards (needed now) or generic Documents (planned later) meant copy-pasting the whole thing.

Changes

• New shared module plugins/export-resources/src/document/:
  • actions.ts — generalized exportDocumentContent/importDocumentContent, typed against any { _class, _id, title? } instead of ControlledDocument. Reuses existing downloadBlob/fileNameFromResponse helpers (also fixed a synchronous-revokeObjectURL bug there).
  • components/ — DocumentExportFormatPopup, DocumentImportFormatPopup, DocumentImportDiffPopup.svelte.
• @hcengineering/export (plugins/export/src/plugin.ts): new component ids + 13 strings, namespaced to avoid collision with the existing (unrelated) CSV/table-export Export/ExportFailed/Import strings. Translated to all 14 locales.
• Controlled documents: models/controlled-documents/src/index.ts now points its Export/Import actions at the shared components. Removed the now-dead docxActions.ts, Export/ImportFormatPopup.svelte, ImportDocxPopup.svelte, and their orphaned ids/strings (12 keys, all 14 lang files).
• Cards: two new actions in models/card/src/actions.ts — "Export content" / "Import content" (distinct label from the existing CSV ExportTable action to avoid two ambiguous "Export" menu items).
• Server: no changes needed — pod-export's exportDocumentHandler already resolves the collaborative field generically by the name content, which Card also uses.
• Documents (generic, non-controlled): out of scope, planned as a follow-up — wiring will just be two more createAction calls against the shared components.