Python v2 worker should surface trigger-binding rejections as explicit ERROR logs (and avoid full-app silent drop)

## Summary

We hit a catastrophic silent failure mode in Python v2 function indexing: a single trigger-binding parameter mismatch (`_req` instead of `req` on `@app.route`) caused the worker to effectively drop registration for the whole app (all routes 404), with no actionable ERROR log pointing to the offending function.

## Minimal repro shape

```python
import azure.functions as func

app = func.FunctionApp(http_auth_level=func.AuthLevel.ANONYMOUS)

@app.function_name(name="health")
@app.route(route="health", methods=[func.HttpMethod.GET])
async def health(_req: func.HttpRequest) -> func.HttpResponse:
return func.HttpResponse("ok")
```

With `_req` (or other non-binding name), production indexing rejects registration. Local unit tests using `app.get_functions()` can still appear green, which makes this hard to catch pre-deploy.

## Requested improvements

1. **Log binding rejections at ERROR level with function-level detail.**
Example expected message:

`ERROR: Function 'health' rejected: @app.route expects first parameter 'req', got '_req'. Function not registered.`

2. **Avoid all-or-nothing registration failure.**
Prefer registering valid functions and skipping only invalid ones (with explicit logs), instead of ending in an apparent "0 functions" state for the full app.

3. **Validate binding-name mismatches earlier (decoration-time / `app.get_functions()` path).**
Today this mismatch can slip through local tests and fail only in deployed worker indexing.

## Why this matters

This is a high-severity operator experience issue: a one-character source bug can lead to full app outage with no direct diagnostic surface to localize root cause quickly.

## References

- Internal incident + remediation ticket: TED-1910
- Fix PR in our repo (one-character change): https://github.com/tedmalone/Tsunami/pull/680
- Follow-up runbook/audit docs documenting the failure mode: https://github.com/tedmalone/Tsunami/pull/681

Start with the Python v2 indexing and app.get_functions() paths described in the issue, using the provided @app.route example to reproduce the binding-name mismatch. Done means invalid functions produce explicit function-level ERROR logs, valid functions remain registered, and the mismatch is detected before deployment.

索引モデルが issue の本文から書いたものです。