feat(webview): native scale snapshot for page bootstrap

[zackees]

Refs #200. Coordinated with FastLED/cli#242. Stacked on #199; merge lifetime support first.

Expose a frozen lexical kernalWindow.initialScaleFactor creation-time native scale snapshot to trusted page bootstrap. Query the private native dispatcher on the existing creation worker, before the UI closure; script-free routes skip the query. Invalid/unavailable native scale falls back to 1.0. This is not browser zoom/DPR, a live monitor-change feed, native IPC, or a privileged world. Reserve and document the binding. Product zoom arithmetic remains in FastLED.

RED missing context -> GREEN fractional/invalid scale formatting and ordering tests. Real Linux bootstrap initial-load/reload, subframe exclusion, absent IPC, origin rejection and cleanup pass with the new context required. Original script-free close/title/size proof passes. Full GUI-support tests, strict all-target Clippy, dependency isolation, formatting and single-reviewer gate pass. Windows x86-64 MSVC and macOS ARM64 crosschecks pass. Native Windows/DPI/media/render/capture parity remains required before release; FastLED adoption is being validated locally. No dependencies or runtime added.

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Closing as superseded: #220 replayed this stacked FastLED foundation onto current main after the #216 merge diverged, and it has landed.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