add resumeGenerate to agent (#11503)

## Description

<!-- Provide a brief description of the changes in this PR -->

- [x] Add `resumeGenerate` method for resuming agent via generate
- [x] Add `runId` and `suspendPayload` to fullOuput of agent stream
- [x] Fix `suspendedToolRunId: null` sometimes breaking `agent.stream`

## Related Issue(s)

<!-- Link to the issue(s) this PR addresses, using hashtag notation:
#123 -->
#11485 

## Type of Change

- [x] Bug fix (non-breaking change that fixes an issue)
- [x] New feature (non-breaking change that adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
- [ ] Code refactoring
- [ ] Performance improvement
- [x] Test update

## Checklist

- [ ] I have made corresponding changes to the documentation (if
applicable)
- [x] I have added tests that prove my fix is effective or that my
feature works


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Resume suspended agent executions via a new generate-based resume API.
* Agent output now exposes runId and suspendPayload for clearer result
context.

* **Bug Fixes**
* suspendedToolRunId now defaults to an empty string to avoid
null/undefined issues.

* **Tests**
* Added tests covering generate-based suspend/resume flows across tools
and workflows.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Abhi Aiyer <abhiaiyer91@gmail.com>

Author: taofeeq-deru

.changeset/silent-ends-lick.md

@@ -0,0 +1,7 @@
+---
+'@mastra/core': patch
+---
+
+Add `resumeGenerate` method for resuming agent via generate
+Add `runId` and `suspendPayload` to fullOutput of agent stream
+Default `suspendedToolRunId` to empty string to prevent `null` issue

e2e-tests/create-mastra/create-mastra.test.ts

@@ -144,7 +144,7 @@ describe('create mastra', () => {
                 "weatherTool": {
                   "description": "Get current weather for a location",
                   "id": "get-weather",
-                  "inputSchema": "{"json":{"$schema":"https://json-schema.org/draft/2020-12/schema","type":"object","properties":{"location":{"description":"City name","type":"string"}},"required":["location"],"additionalProperties":false}}",
+                  "inputSchema": "{"json":{"$schema":"https://json-schema.org/draft/2020-12/schema","type":"object","properties":{"location":{"type":"string","description":"City name"}},"required":["location"],"additionalProperties":false}}",
                   "outputSchema": "{"json":{"$schema":"https://json-schema.org/draft/2020-12/schema","type":"object","properties":{"temperature":{"type":"number"},"feelsLike":{"type":"number"},"humidity":{"type":"number"},"windSpeed":{"type":"number"},"windGust":{"type":"number"},"conditions":{"type":"string"},"location":{"type":"string"}},"required":["temperature","feelsLike","humidity","windSpeed","windGust","conditions","location"],"additionalProperties":false}}",
                   "requireApproval": false,
                 },