feat: add HTML export, custom diff colors, and various parser bug fixes

[phine-apps]

This PR merges the new features (HTML export and custom highlighting colors) and various markdown/table parsing bug fixes into the main branch. All integration and unit tests are passing (195/195).

Key Features Added

• HTML Export: Added rich-markdown-diff.exportHtml command to export the rendered diff view as a standalone HTML file. It automatically replaces VS Code local asset URIs with public CDNs and guards against acquireVsCodeApi to keep interactions (view toggling, folding) functional in standard web browsers.
• Dynamic Default Filename: Customizes the default export filename based on the active diff panel title.
• Custom Diff Highlight Colors: Added user configurations for insertedColor and deletedColor in package.json to allow customizing diff highlights.
• Default View Mode & Fold Configs: Added defaultViewMode (side-by-side or inline) and defaultFoldUnchanged settings.

Critical Bug Fixes Included

• applyEdit SCM Validation (BUG-07): Fixed scheme validation to allow remote files (vscode-remote, etc.) instead of restricting to file:.
• hasOwnProperty frontmatter safety (BUG-01): Prevented crashes when frontmatter contains hasOwnProperty.
• Asymmetric Table row/cell safety (BUG-03): Added index bounds checks (>= 0 and < length) for cell diffing.
• MDX parser nested tag matching (BUG-02): Regular expression fixes for open/close tags to prevent nesting logic errors.
• ReDoS-safe Attribute Injection (BUG-06): Replaced unsafe regex for injecting data-line with a backtracking-proof pattern.
• Git Blame SHA-256 commit hash parsing (BUG-04): Upgraded git blame parser regex to support 64-character SHA-256 hashes.
• Documentation: Updated README.md to document the new settings and HTML Export feature.