[SENTRY NK] Avoid eager CSSStyleSheet construction in PDF viewer

[jdmcleod]

Summary

Fixes C12-NK: TypeError: Illegal constructor on Safari 16.1 when rm-pdf-viewer is instantiated.

createThemeStyleSheet called new CSSStyleSheet() directly, and _updateThemeColors assigned shadowRoot.adoptedStyleSheets. Both APIs only shipped in Safari 16.4, so on older Safari the element constructor throws — in C12 this happened during Turbo's document.importNode while opening a PDF attachment, breaking the modal entirely.

Fix

• theme-config.js now returns a lazy Lit CSSResult (via the css tag) instead of constructing a CSSStyleSheet; renamed to createThemeStyles to match.
• _updateThemeColors applies styles with Lit's adoptStyles, which uses adoptedStyleSheets where supported and falls back to appending <style> tags where not.
• Bumped version to 0.0.10.

Behavior on modern browsers is unchanged (same adopted-stylesheets path as before). On Safari < 16.4 the viewer now renders instead of crashing — note theme colors there still degrade gracefully since the CSS uses light-dark() (Safari 17.5+).

Tests

• Updated theme-config.test.js for the CSSResult return type.
• Added a regression test that replaces globalThis.CSSStyleSheet with a throwing constructor (the Safari < 16.4 condition) and asserts createThemeStyles doesn't throw.
• Full suite: 53 passed. yarn build output verified free of direct new CSSStyleSheet() calls.

Fixes C12-NK

🤖 Generated with Claude Code

https://claude.ai/code/session_019rfbyCarrFPKUsY5mdq3rJ