chore(release): prepare 0.5.0

[moonyue-w]

Summary

Prepare version 0.5.0 for the merged Forward SAT management and Realtime Beta APIs. Align package metadata and current version examples, move the existing release notes into 0.5.0, and retain an empty Unreleased section. Document that Realtime SA access requires a Forward-issued bound SAT and a Realtime-enabled Template.

Why

The release workflow validates the requested version against the source metadata and extracts the matching changelog section. These changes make the merged features ready for the 0.5.0 release.

Verification

• make check-version VERSION=0.5.0
• make lint
• make build
• make test
• make docs-check
• go build ./examples/...
• Account-backed integration tests run, or not required: prior feature validation covers base 5706ff0bd94c4ea764112b3fff1c76b246900dc2; no business implementation changed here.

Changelog validation, 0.5.0 release-note extraction, and all 19 release-script tests passed. No public Go proxy request was made for the not-yet-created v0.5.0 tag.

Impact

• Public API or behavior changed
• User-facing changelog updated: release preparation moves existing entries from Unreleased to 0.5.0.
• Generated API documentation updated (not required; consistency check passed)
• Forward/Managed contract fixtures updated (not required)
• Python and TypeScript parity considered: coordinated 0.5.0 preparation
• Migration notes added for a breaking change (not required)
• No credentials, .env.live, logs, or generated test output committed

This PR changes release metadata and documentation only; it does not change API behavior, retry policy, or test assertions. No new contract fixtures or migration instructions are needed for this version preparation. Live validation was performed against the feature baseline before the version bump; local package checks do not replace public-registry verification after publishing.

Intermittent Realtime service timeouts and transcription/connection failures were observed during earlier live runs. Subsequent runs passed; this version preparation does not claim those service issues are fixed.