First step of the Phase 5 split plan from issue #496. The 14-line title
+ date block becomes its own component named after the visual region.
TDD red/green: DocumentTopBarTitle.svelte.test.ts written first
(7 tests covering title, originalFilename fallback, empty-string
fallback, short-date rendering, no-date branch, title attribute
sourcing). After the test was red the component was created.
DocumentTopBar.svelte updated to use it; the existing 18-test suite
still passes.
Refs #496.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
