[All] Customizable user-agent via application name option

[teodordelibasic-db]

Goal

Let users set an application name when constructing the SDK. The SDK appends it to the identifier it sends in the request header (user-agent), so callers can be identified server-side. Bring this to parity across all SDKs.

Rust is the reference implementation: ZerobusSdkBuilder::application_name (PR #268), also exposed over the FFI in PR #358.

Status

• Rust: done (PR [Rust] Add ZerobusSdkBuilder::application_name for x-zerobus-sdk header #268)
• Go: in progress — tracked by [All] Support CallerOrg in Go SDK to identify callers in x-zerobus-sdk header #194 (PR [Go] Add WithApplicationName method to SdkOption #357)
• Python, TypeScript, Java: to do

Notes

Per-SDK work is tracked in the sub-issues. #194 (CallerOrg) is the Go ticket — it predates application_name and asks for the same capability; PR #357 implements it.