Phase 7E: Preferences onboarding UI (match score, limits, cooldown)

## Phase 7E — Preferences Onboarding UI ### Context Step 2 of the onboarding wizard. Users control how aggressively Scout searches and engages on their behalf. ### Design philosophy **Light. Precise. Technical. Quiet.** ### Scope Create `apps/web/src/pages/onboarding/Preferences.tsx` **Fields:** - Minimum match score (slider: 0–100, default 70, label shows current value) - Maximum daily engagements (number input: 1–20, default 5) - Cooldown between comments (select: 30 min / 1 hr / 2 hr / 4 hr, default 1 hr) - Preferred repo size (select: Any / Small / Medium / Large) **Warning when daily limit > 10:** > Setting this above 10 may trigger GitHub's abuse detection. Recommended maximum: 5. **On submit:** Save to `autonomy_policies` table, navigate to Autonomy step. ### Acceptance criteria - [ ] Component exists at correct path - [ ] All fields work correctly - [ ] Warning appears and is visible when daily limit > 10 - [ ] Defaults pre-populated - [ ] Saves correctly on submit - [ ] Follows design philosophy