Foundation: route, recharts, sprint-dates migration, chart-colors helper (#46)

* feat(ST-1201): add Sprint start_date/end_date + claude_jobs index migration

- Sprint model: optionele start_date en end_date (DATE) voor burndown x-as
- CREATE INDEX claude_jobs(status, finished_at) voor agent-throughput-queries
- Bestaande sprints houden NULL; burndown skipt die

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(ST-1202): add lib/chart-colors.ts + vitest coverage

MD3-token-to-CSS-var mappings for STATUS, PRIORITY, VERIFY, JOB_STATUS
and SERIES_COLORS; all 5 tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(ST-1203): add Insights link to NavBar

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(ST-1204): move Insights NavBar link between Solo and Todo's

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(ST-1205): add sprint start_date/end_date UI + server actions

- createSprintAction + updateSprintDatesAction: Zod date validation
  with end_date >= start_date cross-check
- start-sprint-button: date inputs in create dialog
- sprint-header: date display button + edit dialog with updateSprintDatesAction
- sprint page: select start_date/end_date for SprintHeader prop
- Demo blokkade via bestaande isDemo checks
- 6 tests groen (validation + demo guard)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

components/shared/nav-bar.tsx

@@ -137,6 +137,7 @@ export function NavBar({
                 pathname.includes('/solo')
               )
             : disabledSpan('Solo')}
+          {navLink('/insights', 'Insights', pathname.startsWith('/insights'))}
           {navLink('/todos', "Todo's", pathname.startsWith('/todos'))}
         </nav>
       </div>