onSchedule() with string parameter creates Cloud Scheduler jobs with incorrect v1 URLs instead of v2 Cloud Run URLs

### [REQUIRED] Environment info
**firebase-functions:** 6.4.0
**firebase-tools:** 14.16.0
**Platform:** macOS (Darwin 25.0.0)

### [REQUIRED] Test case

```typescript
import { onSchedule } from 'firebase-functions/v2/scheduler'

// This FAILS - creates scheduler with wrong URL format
export const failingScheduler = onSchedule(
'every 1 minutes',
async () => {
console.log('This function gets PERMISSION_DENIED')
}
)

// This WORKS - creates scheduler with correct URL
export const workingScheduler = onSchedule(
{
schedule: 'every 1 minutes',
timeZone: 'America/Los_Angeles',
},
async () => {
console.log('This function works correctly')
}
)
```

### [REQUIRED] Steps to reproduce

1. Create a v2 scheduled function using the string parameter syntax
2. Deploy with `firebase deploy --only functions`
3. Check Cloud Scheduler console
4. Observe the scheduler job has URL: `https://us-central1-PROJECT.cloudfunctions.net/FUNCTION_NAME` (v1 format)
5. Function execution fails with `PERMISSION_DENIED`

### [REQUIRED] Expected behavior

Both syntaxes should create Cloud Scheduler jobs with the correct v2 Cloud Run URLs (format: `https://FUNCTION_NAME-HASH-uc.a.run.app/`)

### [REQUIRED] Actual behavior

When using the string parameter syntax, Cloud Scheduler jobs are created with v1 function URLs that don't exist, causing `PERMISSION_DENIED` errors.

Cloud Scheduler shows:
- Functions with string syntax: URL points to `cloudfunctions.net` (v1) - **FAILS**
- Functions with object syntax: URL points to `run.app` (v2) - **WORKS**

### Analysis

The TypeScript types allow both signatures:
```typescript
onSchedule(schedule: string, handler: Function)
onSchedule(options: ScheduleOptions, handler: Function)
```

However, only the object syntax properly configures the Cloud Scheduler job with the correct Cloud Run URL. This is a critical bug because:

1. The types suggest both are valid
2. The deployment succeeds without warnings
3. The error only appears at runtime when scheduler tries to invoke the function
4. The error message (`PERMISSION_DENIED`) doesn't indicate the root cause is a URL mismatch

### Workaround

Always use the object syntax with explicit `schedule` and `timeZone` properties:

```typescript
onSchedule({
schedule: 'every 1 minutes',
timeZone: 'America/Los_Angeles',
}, handler)
```

### Related Issues

This appears related to:
- #1425 (PERMISSION_DENIED errors)
- #1447 (Cloud Function V2 not creating deterministic Function URL)
- #1293 (V2 scheduled functions deployment issues)

Start at the TypeScript onSchedule(string, handler) entry point and compare it with the object overload. Deploy both forms with firebase deploy --only functions, then verify that the string form creates the same v2 Cloud Run URL as the object form and no longer causes PERMISSION_DENIED in Cloud Scheduler.

Written by the indexing model from the issue text.