Fix onboarding bypass, tasks header UI, and auth gaps

[stephenhungg]

Summary

• Closes the onboarding bypass where returning drivers with no partner_id could skip partner selection and land on an empty task list
• Fixes a race condition in ProfileContext that caused returning drivers to briefly flash to onboarding on cold start
• Fixes the tasks page header to be visually flush with the top of the screen (matching the home page)
• Fixes spacing and alignment issues within the tasks page header
• Adds vendor/ to .prettierignore so bundled Ruby gems don't fail the pre-commit hook

Changes

src/app/index.tsx

After confirming auth, now checks profile?.partner_id from ProfileContext. If the driver has no partner set, redirects to /onboarding instead of /(tabs)/my-tasks. This catches:

• Fresh signups who haven't completed onboarding
• Returning drivers who signed up but never finished partner selection

src/utils/ProfileContext.tsx

• Initialize loading as true (was false) so index.tsx waits for the first profile fetch before making a routing decision
• clearProfile() now sets loading = false so unauthenticated users don't spin forever

src/app/(tabs)/available-pick-ups.tsx

• Removed SafeAreaView wrapper — it was double-stacking top insets (SafeAreaView's automatic padding + paddingTop: 58 in the header), causing a gray gap behind the status bar and the header appearing pushed down
• Now uses a plain View matching the same pattern as the home page

src/styles/tabs/available-pick-ups-styles.ts

• Header paddingBottom: 20 → 14
• dateHeaderText marginTop: 12 → 8, marginBottom: 16 → 12
• contentContainer paddingBottom: 24 → 140 to clear the tab bar and home indicator

src/components/AnimatedSegmentedControl.tsx

• marginHorizontal: 26 → 0 so the pill aligns with the header text instead of being double-inset (header padding + component margin)
• marginBottom: 23 → 0, added marginTop: 12 for spacing from the subtext above

.prettierignore

Added vendor/ to exclude the bundled Ruby gems directory from prettier checks

Test plan

• Cold start as an authenticated driver with partner_id set → goes directly to tasks tab
• Cold start as an authenticated driver with no partner_id → redirected to onboarding
• Fresh signup → onboarding → select partner → lands on tasks tab
• Tasks page header is flush with the top of the screen (no gray gap behind status bar)
• Today/Tomorrow pill spans the full width of the header content
• Spacing between pill and list content is tight, not a 55px gap
• Pre-commit hook passes (pnpm run prettier:check)