Embed kitchen sink fixture in Trusted Server

[ChristianPavilonis]

Summary

Add a built-in Trusted Server kitchen-sink fixture that can be enabled by config and served from /_ts/kitchen-sink/.

Scope

• Add debug.kitchen_sink_enabled, defaulting to false.
• Embed the migrated kitchen-sink static site in a new crate.
• Serve HTML through Trusted Server's HTML processing pipeline.
• Serve non-HTML assets raw with cache/security headers.
• Route kitchen-sink requests before asset-route and publisher fallback.
• Cover config, asset, handler, and adapter dispatch behavior with tests.

Verification

• cargo fmt --all -- --check
• cargo test --workspace
• cargo test --package trusted-server-adapter-fastly kitchen_sink -- --nocapture
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo build --package trusted-server-adapter-fastly --release --target wasm32-wasip1
• cd docs && npx prettier --check .