feat(config): bounded TOML documents with owned values

[zackees]

Scope

Refs #206. Adds optional config-toml with private exact TOML implementation and facade-owned Document, Value, and ParseError. Applications retain schema validation, defaults, and unknown-field policy. Source bytes are bounded before parsing; decoded node/depth limits are enforced after parsing, explicitly documented.

Validation

• RED: missing kernal_api::config import; GREEN: three focused contract tests.
• Full config-toml feature test suite, strict all-target Clippy, formatting, and dependency isolation passed.
• Windows MSVC and macOS ARM cross-checks passed using Soldr with cache disabled after cached relay failures.
• Python Ruff and read-only review passed.
• Normal-runtime TOML edges are absent by default and present with the feature; the existing build-time TOML dependency is not misrepresented as absent.

Coordination

Coordinated with FastLED/cli#242. Stacked on #205; land this capability before releasing and adopting the published app dependency. FastLED adoption and its real WASM compile verification are pending.

[zackees]

FastLED adoption is implemented in FastLED/cli#242 (2dfaf35). Both TOML call sites now use Document; direct manifest/lockfile edges removed. App-owned schema regression tests passed before and after; dependency boundary RED→GREEN. All 268 Rust tests, 31 Python tests (1 skipped), strict all-target Clippy, formatting, Ruff, and real fresh-sketch WASM compile passed. No JSPI entry points found in generated JS; browser/Safari acceptance remains separate. Current upstream dylints failure is setup-soldr nightly catalog digest mismatch, before source linting; integrity validation was not bypassed.

[zackees]

Closing as superseded: #220 replayed this stacked FastLED foundation onto current main after the #216 merge diverged, and it has landed.

Verified against origin/main (e0666e0): every file this PR's own commits add exists on main, and every distinctive added source/test line is present on main (one JSON doc-comment line was reworded). Merging this branch now would only reintroduce pre-refactor code that main has since replaced.

Reopen if something here is still missing from main.