feat: add daily/weekly goals, streaks, and time rounding

Settings Timer tab now has daily/weekly goal hour inputs. Dashboard
shows goal progress bars and streak counter. Settings Billing tab
has rounding toggle with increment and method selectors. New
rounding.ts utility for nearest/up/down time rounding.

src/utils/rounding.ts

@@ -0,0 +1,10 @@
+export function roundDuration(seconds: number, incrementMinutes: number, method: 'nearest' | 'up' | 'down'): number {
+  if (incrementMinutes <= 0) return seconds
+  const incSeconds = incrementMinutes * 60
+  switch (method) {
+    case 'up': return Math.ceil(seconds / incSeconds) * incSeconds
+    case 'down': return Math.floor(seconds / incSeconds) * incSeconds
+    case 'nearest': return Math.round(seconds / incSeconds) * incSeconds
+    default: return seconds
+  }
+}