Auto-generate binary trigger payload handling from SDK annotations

## Problem

When a developer writes a trigger callback function for a binary-content trigger (e.g., OneDrive OnNewFileV2), they must manually write JsonDocument inspection code to detect the body field type and decode base64 content. This boilerplate is error-prone and non-obvious.

The AI Gateway sends binary triggers as JSON with a base64 string body:
- Binary: {"body":""}
- Metadata: {"body":{"value":[{...typed items...}]}}

Both arrive with Content-Type: application/json, so content-type sniffing does not work.

## Proposed Solution

When the LSP detects a [ConnectorTriggerMetadata] attribute referencing a binary-content trigger operation, it should:

1. Offer a CodeAction/CodeLens to generate the binary payload handling boilerplate
2. Generate the JsonDocument body-type inspection pattern
3. Generate the base64 decode + byte array extraction
4. Warn if the developer uses a typed TriggerCallbackPayload deserializer on a binary trigger

## Prerequisites

This depends on Azure/Connectors-NET-SDK#51 - the SDK needs to annotate trigger operations as binary vs metadata before the LSP can act on them.