Changes

src/biscuit/editor/text/ts_highlighter.py — The Tree-sitter highlighting engine:

• TreeSitterHighlighter class with full/incremental parsing
• highlight() — Full parse for file load/language change
• incremental_highlight(edit_info) — Uses tree.edit() + parser.parse(old_tree) + changed_ranges() to only re-highlight what changed
• Language detection via extension map (78 extensions) and alias map (62 aliases)
• Display names for 47 languages in the statusbar
• Graceful fallback to plain text for unsupported languages

src/biscuit/editor/text/queries/<lang>/highlights.scm — Highlight queries for 25 languages:
bash, c, cpp, csharp, css, go, html, java, javascript, json, kotlin, lua, markdown, php, python, ruby, rust, scala, sql, swift, toml, tsx, typescript, yaml, zig

src/biscuit/editor/text/highlighter.py — Pygments completely commented out, replaced with thin wrapper delegating to TreeSitterHighlighter. Original Pygments implementation preserved as comments.

src/biscuit/editor/text/text.py — Wired incremental parsing:

• _proxy() captures edit positions (byte offsets + row/col points) before/after each insert/delete/replace
• refresh() uses incremental_highlight() when edit info is available, falls back to full highlight() otherwise
• Refactored _proxy() to stay within complexity limit

src/biscuit/settings/theme/theme.py — Added treesitter_syntax dict mapping 55 Tree-sitter capture names (@keyword, @string, @function, etc.) to existing theme color variables. All 6 themes inherit automatically.