feat: add recurring invoices, public links, time tracker, payments, reminders

- Recurring invoices: schedule-based auto-generation with CRUD UI at /dashboard/invoices/recurring and POST /api/cron/generate-recurring cron endpoint
- Public invoice link: generate/revoke shareable /i/[token] page for unauthenticated clients with PDF download
- Live time tracker: localStorage-persisted timer widget in invoice editor that appends a line item on stop (rounds to nearest 0.25h)
- Partial payment tracking: record payments per invoice, auto-mark paid when fully covered, balance due display
- Send reminder: email reminder via Resend with custom message dialog and last-sent indicator

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

src/components/invoice/time-tracker.tsx

@@ -0,0 +1,136 @@
+"use client";
+
+import { useEffect, useRef, useState } from "react";
+import { Play, Square } from "lucide-react";
+import { Button } from "~/components/ui/button";
+import { Input } from "~/components/ui/input";
+
+interface TimeTrackerProps {
+  invoiceId: string;
+  onStop: (hours: number, description: string) => void;
+  defaultRate?: number;
+}
+
+interface PersistedState {
+  running: boolean;
+  startedAt: number | null;
+  description: string;
+}
+
+function storageKey(invoiceId: string) {
+  return `time-tracker-${invoiceId}`;
+}
+
+function formatElapsed(seconds: number) {
+  const h = Math.floor(seconds / 3600);
+  const m = Math.floor((seconds % 3600) / 60);
+  const s = seconds % 60;
+  return [h, m, s].map((v) => String(v).padStart(2, "0")).join(":");
+}
+
+function readPersistedState(invoiceId: string): PersistedState {
+  if (typeof window === "undefined") return { running: false, startedAt: null, description: "" };
+  try {
+    const raw = localStorage.getItem(storageKey(invoiceId));
+    if (raw) return JSON.parse(raw) as PersistedState;
+  } catch {
+    // ignore
+  }
+  return { running: false, startedAt: null, description: "" };
+}
+
+export function TimeTracker({ invoiceId, onStop }: TimeTrackerProps) {
+  const [running, setRunning] = useState(() => readPersistedState(invoiceId).running);
+  const [startedAt, setStartedAt] = useState<number | null>(
+    () => readPersistedState(invoiceId).startedAt,
+  );
+  const [elapsed, setElapsed] = useState(() => {
+    const s = readPersistedState(invoiceId);
+    if (s.running && s.startedAt) {
+      return Math.max(0, Math.floor((Date.now() - s.startedAt) / 1000));
+    }
+    return 0;
+  });
+  const [description, setDescription] = useState(
+    () => readPersistedState(invoiceId).description,
+  );
+  const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
+
+  useEffect(() => {
+    if (running && startedAt !== null) {
+      intervalRef.current = setInterval(() => {
+        setElapsed(Math.floor((Date.now() - startedAt) / 1000));
+      }, 1000);
+    }
+    return () => {
+      if (intervalRef.current) clearInterval(intervalRef.current);
+    };
+  }, [running, startedAt]);
+
+  function persist(state: PersistedState) {
+    localStorage.setItem(storageKey(invoiceId), JSON.stringify(state));
+  }
+
+  function handleStart() {
+    const now = Date.now();
+    setStartedAt(now);
+    setElapsed(0);
+    setRunning(true);
+    persist({ running: true, startedAt: now, description });
+  }
+
+  function handleStop() {
+    if (intervalRef.current) clearInterval(intervalRef.current);
+    const hours = Math.max(0.25, Math.ceil(elapsed / 900) * 0.25);
+    setRunning(false);
+    setStartedAt(null);
+    setElapsed(0);
+    localStorage.removeItem(storageKey(invoiceId));
+    onStop(hours, description);
+    setDescription("");
+  }
+
+  return (
+    <div className="bg-secondary flex flex-col gap-3 rounded-lg p-3 sm:flex-row sm:items-center">
+      {running ? (
+        <>
+          <span className="text-primary font-mono text-xl font-bold tabular-nums">
+            {formatElapsed(elapsed)}
+          </span>
+          <Input
+            value={description}
+            onChange={(e) => {
+              setDescription(e.target.value);
+              persist({ running: true, startedAt, description: e.target.value });
+            }}
+            placeholder="What are you working on?"
+            className="flex-1"
+          />
+          <Button type="button" variant="default" size="sm" onClick={handleStop} className="shrink-0">
+            <Square className="mr-1 h-3.5 w-3.5" />
+            Stop & add
+          </Button>
+        </>
+      ) : (
+        <>
+          <Input
+            value={description}
+            onChange={(e) => setDescription(e.target.value)}
+            placeholder="What will you work on?"
+            className="flex-1"
+            onKeyDown={(e) => {
+              if (e.key === "Enter") {
+                e.preventDefault();
+                handleStart();
+              }
+            }}
+          />
+          <Button type="button" variant="secondary" size="sm" onClick={handleStart} className="shrink-0">
+            <Play className="mr-1 h-3.5 w-3.5" />
+            Start timer
+          </Button>
+        </>
+      )}
+    </div>
+  );
+}