CMake: enable C (Homebrew LLVM's config needs it); Kate: highlighting, language server setup, install script

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

editors/kate/README.md

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+# Finch in Kate
+
+Syntax highlighting and the Finch language server for **Kate** (and KWrite / KDevelop, which share
+Kate's highlighting engine).
+
+## Install
+
+```sh
+editors/kate/install.sh
+```
+
+It copies `finch.xml` to `~/.local/share/org.kde.syntax-highlighting/syntax/` and adds a `finch` entry
+to `~/.config/kate/lspclient/settings.json` (your other servers are kept). Then:
+
+1. Restart Kate.
+2. **Settings → Configure Kate → Plugins**: enable **LSP Client** (and **Build & Run** for the next part).
+3. Make sure `finch` is on your PATH (`finch version` in a terminal).
+
+Open a `.fch` file: errors appear as you type, hovering shows types and docs, `Ctrl+Space` completes
+(fields and methods after `.`), **Go to Definition** and the **Symbols** outline work, and parameter hints
+pop up inside `(…)`.
+
+## Running and building
+
+**Build & Run** plugin → **Add target set**, then add targets with these commands (the working folder
+can be `%d`, the folder of the current file):
+
+| Target | Command |
+|---|---|
+| Run | `finch run %f` |
+| Build | `finch build %f` |
+
+Give one of them a shortcut in **Settings → Configure Keyboard Shortcuts** (search for "Build"). Finch's
+errors have the `file:line:column: error:` form, so Kate lists them and jumps to the line on click.
+
+## By hand
+
+- Highlighting: copy `finch.xml` into `~/.local/share/org.kde.syntax-highlighting/syntax/`
+  (Windows: `%LOCALAPPDATA%\org.kde.syntax-highlighting\syntax\`).
+- Language server: **Settings → Configure Kate → LSP Client → User Server Settings**, and add the
+  `finch` entry from `lspclient.json` inside `"servers"`.