Embed kitchen sink fixture in Trusted Server

[ChristianPavilonis]

Summary

• Embed the kitchen-sink fixture in Trusted Server behind debug.kitchen_sink_enabled.
• Serve the fixture at /_ts/kitchen-sink/ with processed HTML and raw static assets.
• Add tests and design/implementation docs for the new built-in fixture path.

Changes

File	Change
Cargo.toml, Cargo.lock	Add trusted-server-kitchen-sink workspace crate.
crates/trusted-server-kitchen-sink/	Add embedded static-site crate, build-time recursive asset generation, migrated kitchen-sink files, content types, and asset tests.
crates/trusted-server-core/src/kitchen_sink.rs	Add core kitchen-sink handler with config gating, trailing-slash redirect, exact asset routing, HTML processing, raw asset serving, cache/security headers, ETags, and tests.
crates/trusted-server-core/src/settings.rs	Add debug.kitchen_sink_enabled default-off config with parse/default/unknown-field tests.
crates/trusted-server-adapter-fastly/src/app.rs	Wire kitchen-sink dispatch before asset routes/publisher fallback on the EdgeZero path and add dispatch precedence tests.
crates/trusted-server-adapter-fastly/src/main.rs	Wire equivalent kitchen-sink handling on the legacy route path.
trusted-server.example.toml	Document the disabled-by-default kitchen-sink debug flag.
docs/superpowers/specs/2026-06-23-embedded-kitchen-sink-design.md	Add design spec for the embedded kitchen-sink site.
docs/superpowers/plans/2026-06-23-embedded-kitchen-sink-implementation-plan.md	Add implementation plan.

Closes

Closes #815

Test plan

• cargo test --workspace
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• JS tests: cd crates/trusted-server-js/lib && npx vitest run
• JS format: cd crates/trusted-server-js/lib && npm run format
• Docs format: cd docs && npm run format
• WASM build: cargo build --package trusted-server-adapter-fastly --release --target wasm32-wasip1
• Manual testing via fastly compute serve
• Other: cargo test --package trusted-server-adapter-fastly kitchen_sink -- --nocapture
• Other: cd docs && npx prettier --check .
• Other: git diff --check

Checklist

• Changes follow CLAUDE.md conventions
• No unwrap() in production code — use expect("should ...")
• Uses project logging macros (not println!)
• New code has tests
• No secrets or credentials committed

[ChristianPavilonis]

should look into flagging auctions in the kitchen sink as a test.