Fix macOS settings card contrast

[pttydou]

What

• detect the macOS settings route through data-settings-panel-slug
• mark only large, opaque, high-luminance native settings surfaces
• apply a scoped dark semantic text palette to those verified light cards
• clear renderer-owned markers after route changes, hot reinjection, and restore
• add macOS regression coverage and an unreleased changelog entry

Why

New Codex macOS settings panels can retain native white cards inside the dark Terraria shell. The previous light inherited text then loses contrast. The fix keeps the native cards intact and restores readable text without globally recoloring Markdown, navigation, or other dark surfaces.

Impact

• macOS only
• Windows source is unchanged
• no official Codex application files, app.asar, signatures, or user projects are modified
• no Release is created by this PR

Validation

• PASS: renderer injection regression suite
• PASS: image metadata, injector bootstrap, theme staging, companion inventory, and injector payload checks under bundled Node on Windows
• PASS: git diff --check
• macOS live DOM verification remains to be performed on a Mac after review