Fix spec compliance gaps in email and dashboard

- Email subject now follows spec format: PhaseFlow: [STATUS] - Day [cycleDay] ([phase])
- Daily email includes seed switch alert on day 15 (using getSeedSwitchAlert)
- Data panel HRV status now color-coded: green=Balanced, red=Unbalanced, gray=Unknown
- Data panel shows progress bar for week intensity vs phase limit with color thresholds

Adds 13 new tests (990 total).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/page.test.tsx

@@ -244,7 +244,7 @@ describe("Dashboard", () => {
       render(<Dashboard />);
 
       await waitFor(() => {
-        expect(screen.getByText(/hrv.*balanced/i)).toBeInTheDocument();
+        expect(screen.getByTestId("hrv-status")).toHaveTextContent("Balanced");
       });
     });