Add template and ticket release APIs

[pietechsolution]

What changed

• adds the public template-instantiation resource
• adds ticket-release list, whole-list replacement, and close operations
• preserves exact header replay for template instantiation
• keeps ticket-release writes deliberately single-attempt
• updates types, URI-escaping coverage, quickstarts, changelog, and local 0.4.0 candidate metadata where applicable

Why

The central SeatLayer candidate exposes four stable existing capabilities that need complete official server-SDK coverage.

Impact

Source candidate only. This PR does not tag or publish the SDK.

Validation

• repository-prescribed lint, type, test, build, and package checks
• focused path, body, identifier-escaping, and retry-policy coverage