fix: stabilize Gemini formatting and selected-text copy (5.0.5)

[kangjoseph90]

Gemini paragraphs containing PNG/source chips previously skipped all repair, leaving broken Markdown/LaTeX and configured bold colors unapplied. Version 5.0.5 repairs surrounding text while keeping original citation/response widgets live, and includes the follow-up rendering and selected-copy fixes in this same version.

• Preserve links, controls, and nested mixed text/widget spans through manual slots on existing hosts. Original nodes, attributes, parents, handlers, and component lifecycle remain intact. Structural widget arrival renders before paint; retained nested hosts continue repairing after widget removal; disable/fallback/destroy retain minimal native passthrough.
• Reconstruct composed selected ranges for HTML and plain-text copy, including partial formatting, multiple shadow paragraphs, and live slotted citations. Exclude hidden originals and duplicate KaTeX MathML. Native/editor/button selections keep their original copy path; MathML remains accessible.
• Support inert sanitizer metadata, dir-split tokens, native CSS/theme updates, boxed spans, sup/sub/mark, currency unit suffixes, display/custom math finalization, and bare text-only lists projected through their existing supported parent. Shared extension/userscript engine remains 5.0.5; README stays concise.

Validation: all 91 browser tests pass (19 added to the initial citation fix), including real MV3 popup/storage integration, retained source identity, widget focus/handlers/lifecycle, streaming completion/toggles, list layout, and pointer-selected copy across shadow/native boundaries. Copy tests use mocked ClipboardEvents. Generated userscript consistency and git diff checks pass. Updated the installed test extension and verified the reported live Gemini paragraph: configured bold color applies and the original PNG source popup opens by keyboard. Streaming edge cases are verified with simulated Gemini DOM updates.