feat(export): add .toml source download and shared slugify helper

src/composables/useSourceExport.test.ts

@@ -0,0 +1,13 @@
+import { describe, it, expect } from 'vitest'
+import { sourceFilename } from './useSourceExport'
+
+describe('sourceFilename', () => {
+  it('slugifies the plan title into a .toml name', () => {
+    expect(sourceFilename('Q3 — Checkout revamp')).toBe('macroplan-q3-checkout-revamp.toml')
+  })
+
+  it('falls back to a generic name when the title has no usable characters', () => {
+    expect(sourceFilename('')).toBe('macroplan-plan.toml')
+    expect(sourceFilename('—— ··')).toBe('macroplan-plan.toml')
+  })
+})