Pass 4 — Copy to Clipboard and .txt Export from GeneratedDraftPreview

The `GeneratedDraftPreview` card already rendered the full note draft as selectable text. What was missing was a one-tap copy path and a durable local export. Pass 4 adds both.

VaultStore.swift received `exportNoteDraft(for sessionID: UUID)`, placed immediately before `exportBackup()` so the two export methods stay grouped. The method:

1. Locates the session by ID via `vaultData.sessions.first(where:)`. 2. Reads `session.generatedDraftPreview` — the same computed string already rendered in the card. 3. Constructs a filename of the form `ConCOREdance_Draft_<sanitized_name>_<timestamp>.txt`. Name sanitization joins whitespace-separated components with underscores. The timestamp format reuses the existing `Self.fileStamp` formatter. 4. Writes the text to `~/Downloads` using `String.write(to:atomically:encoding:)` with `.utf8`. 5. On success: calls `audit("Note draft exported: \(session.caseReference.displayName)")` and `save()`, then sets `alertMessage = "Draft note saved to Downloads."`. 6. On failure: sets `alertMessage` with the localized error.

This mirrors `exportBackup()` structurally. The distinction is that the draft export writes plain text (not the encrypted vault), and it audits the event — plain text leaving the app is meaningful in a clinical context.

Views.swift required two changes.

`import AppKit` was added at the top of the file alongside `import SwiftUI`. This provides explicit access to `NSPasteboard` and aligns with macOS 14 as the declared platform target.

`GeneratedDraftPreview` was updated:

• `@EnvironmentObject private var vaultStore: VaultStore` was added. The view is only used within `ActiveSessionWorkspace`, which already has VaultStore in the environment via `MainWorkspaceView`.
• `@State private var copyConfirmed = false` was added for the confirmation state.
• The header `HStack` was extended with two new controls placed after the existing artifact status label:
• Copy button: calls `NSPasteboard.general.clearContents()` and `NSPasteboard.general.setString(session.generatedDraftPreview, forType: .string)`, then sets `copyConfirmed = true` and schedules a reset after 1.8 seconds via `DispatchQueue.main.asyncAfter`. Label and icon toggle between "Copy" / `doc.on.doc` and "Copied" / `checkmark`, foreground color transitions to `palette.aurora` on confirmation. Animated with `.snappy(duration: 0.18)`.
• Export button: calls `vaultStore.exportNoteDraft(for: session.id)`. Label is "Export .txt" with `arrow.down.doc` icon. No confirmation state — the VaultStore `alertMessage` serves as confirmation.

Both buttons use `.buttonStyle(.plain)` and `.font(.caption.weight(.medium))` to match the existing inline action style. HStack spacing on the header row was set to `12` for consistent breathing room.

VaultStoreTests.swift received two new test methods in a `// MARK: — Export Note Draft` section:

`testExportNoteDraftSetsSuccessAlert` calls `exportNoteDraft` and asserts that `alertMessage` is non-nil and contains "Downloads". The actual file write goes to the real `~/Downloads` during test execution — the same approach as `exportBackup()`, which is also untested at the file level. The filename's timestamp ensures no collision between runs.

`testExportNoteDraftAddsAuditEvent` confirms that the audit event count increases after the export call.

Tests do not verify the `.txt` file content or filename pattern — those are best confirmed by visual inspection during Cody's integration run.