feat(web): add custom pre-warning messages per timer

- Add customMessage field to Timer interface + all Create*Params
- Custom message input in CreateTimerModal (optional, non-pomodoro)
- TimerCard shows custom message, falls back to auto-generated prep tips
- 373/373 tests pass, 0 type errors

web/src/components/CreateTimerModal.tsx

@@ -47,6 +47,9 @@ export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
   // Event fields
   const [eventDate, setEventDate] = useState('');
 
+  // Custom pre-warning message
+  const [customMessage, setCustomMessage] = useState('');
+
   // Validation errors
   const [errors, setErrors] = useState<Record<string, string>>({});
 
@@ -128,6 +131,7 @@ export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
         urgency,
         cascade,
         category: catOrUndef,
+        customMessage: customMessage || undefined,
       });
     } else if (tab === 'countdown') {
       const result = countdownSchema.safeParse({ label: label || 'Countdown', hours, minutes, seconds, urgency, cascadePreset });
@@ -144,6 +148,7 @@ export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
         urgency,
         cascade,
         category: catOrUndef,
+        customMessage: customMessage || undefined,
       });
     } else if (tab === 'pomodoro') {
       const result = pomodoroSchema.safeParse({ label: label || 'Focus Session', workMinutes: workMin, breakMinutes: breakMin, longBreakMinutes: longBreakMin, rounds, urgency });
@@ -177,6 +182,7 @@ export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
         targetTime: target,
         urgency,
         category: catOrUndef,
+        customMessage: customMessage || undefined,
       });
     }
 
@@ -188,6 +194,7 @@ export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
     setSeconds(0);
     setCategory('');
     setEventDate('');
+    setCustomMessage('');
     setErrors({});
     onClose();
   };
@@ -511,6 +518,31 @@ export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
             </div>
           )}
 
+          {/* Custom pre-warning message (non-pomodoro) */}
+          {tab !== 'pomodoro' && (
+            <div>
+              <label className="block text-sm font-medium mb-1" style={{ color: 'var(--cm-text-secondary)' }}>
+                Custom Warning Message <span className="text-xs font-normal" style={{ color: 'var(--cm-text-tertiary)' }}>(optional)</span>
+              </label>
+              <input
+                type="text"
+                value={customMessage}
+                onChange={(e) => setCustomMessage(e.target.value)}
+                placeholder='e.g. "Review your agenda" or "Bring your insurance card"'
+                maxLength={200}
+                className="w-full px-3 py-2 rounded-lg border text-sm focus:outline-none focus:ring-2"
+                style={{
+                  backgroundColor: 'var(--cm-surface-card)',
+                  borderColor: 'var(--cm-border)',
+                  color: 'var(--cm-text-primary)',
+                }}
+              />
+              <p className="text-xs mt-1" style={{ color: 'var(--cm-text-tertiary)' }}>
+                Shown in pre-warning notifications instead of auto-generated tips
+              </p>
+            </div>
+          )}
+
           {/* Cascade preset (non-pomodoro) */}
           {tab !== 'pomodoro' && (
             <div>

web/src/components/TimerCard.tsx

@@ -231,8 +231,13 @@ export function TimerCard({ timer }: TimerCardProps) {
         </p>
       )}
 
-      {/* Prep time warning */}
+      {/* Custom message or prep time warning */}
-      {!isDone && !isFiring && (() => {
+      {!isDone && !isFiring && timer.customMessage && (
+        <p className="text-xs mb-3 flex items-center gap-1 font-medium" style={{ color: 'var(--cm-accent-secondary)' }}>
+          💬 {timer.customMessage}
+        </p>
+      )}
+      {!isDone && !isFiring && !timer.customMessage && (() => {
         const prepConfig = getSuggestedPrepTime(timer.label, timer.category);
         const minutesUntil = Math.round(remaining / 60_000);
         if (shouldShowPrepWarning(timer.targetTime, prepConfig, now)) {

web/src/lib/timer-engine.ts

@@ -58,6 +58,7 @@ export interface Timer {
   tags?: string[];
   linkedTimerId?: string | null;
   recurringTimerId?: string | null;
+  customMessage?: string | null;
 }
 
 export interface PomodoroConfig {
@@ -90,6 +91,7 @@ export interface CreateAlarmParams {
   cascade?: CascadeConfig;
   category?: string;
   description?: string;
+  customMessage?: string;
 }
 
 export function createAlarm(params: CreateAlarmParams): Timer {
@@ -118,6 +120,7 @@ export function createAlarm(params: CreateAlarmParams): Timer {
     snoozeCount: 0,
     snoozedUntil: null,
     category: params.category,
+    customMessage: params.customMessage ?? null,
   };
 }
 
@@ -128,6 +131,7 @@ export interface CreateCountdownParams {
   cascade?: CascadeConfig;
   category?: string;
   description?: string;
+  customMessage?: string;
 }
 
 export function createCountdown(params: CreateCountdownParams): Timer {
@@ -157,6 +161,7 @@ export function createCountdown(params: CreateCountdownParams): Timer {
     snoozeCount: 0,
     snoozedUntil: null,
     category: params.category,
+    customMessage: params.customMessage ?? null,
   };
 }
 
@@ -167,6 +172,7 @@ export interface CreateEventParams {
   cascade?: CascadeConfig;
   category?: string;
   description?: string;
+  customMessage?: string;
   milestones?: number[]; // days before event to warn (e.g. [30, 7, 1])
 }
 
@@ -203,6 +209,7 @@ export function createEvent(params: CreateEventParams): Timer {
     snoozeCount: 0,
     snoozedUntil: null,
     category: params.category,
+    customMessage: params.customMessage ?? null,
   };
 }