fix(server): transcript key & bump models (#15485)

#### PR Dependency Tree


* **PR #15485** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

## Summary by CodeRabbit

* **New Features**
* Upgraded built-in AI actions and chat model selection to Gemini 3.7
Flash.
* Transcript attachments now retain storage keys and support secure
presigned URLs during processing.
* Completed transcript results preserve attachment metadata for reliable
access.

* **Bug Fixes**
* Improved transcript handling across uploads, retries, and native
processing.
  * Added safeguards for invalid or missing attachment URLs.

* **Maintenance**
* Added a migration to backfill storage keys for existing transcript
records without altering their URLs.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Cargo.lock

@@ -2963,7 +2963,7 @@ dependencies = [
  "libc",
  "log",
  "rustversion",
- "windows-link 0.2.1",
+ "windows-link 0.1.3",
  "windows-result 0.4.1",
 ]
 
@@ -4756,9 +4756,9 @@ dependencies = [
 
 [[package]]
 name = "llm_adapter"
-version = "0.2.18"
+version = "0.2.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "49df35c253da1563c33f0733ef3a46da3194299807cbd7e03c48dfa12a89a72f"
+checksum = "c17ef06aac72e31a4fae7937998029267c4d923a0671bf1a4062c96a1ab5fa70"
 dependencies = [
  "base64",
  "jsonschema",