Extract kiln-ui: standalone game-agnostic ratatui widget toolkit

Widgets (CodeEditor, TextField, Dialog) plus clipboard/text internals,
extracted from the kiln workspace. No game-engine dependency.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/text.rs

@@ -0,0 +1,71 @@
+//! Small char/width/key helpers shared by the text widgets
+//! ([`code_editor`](crate::code_editor), [`text_field`](crate::text_field)).
+
+use ratatui::crossterm::event::{KeyEvent, KeyModifiers};
+use unicode_width::UnicodeWidthChar;
+
+/// Columns a tab advances to (tab stop).
+pub(crate) const TAB_WIDTH: usize = 4;
+
+/// Byte offset of character index `col` within `s` (clamped to `s.len()`).
+pub(crate) fn byte_of(s: &str, col: usize) -> usize {
+    s.char_indices().nth(col).map_or(s.len(), |(b, _)| b)
+}
+
+/// Display width of `c` at running display column `at` (tabs advance to the next
+/// [`TAB_WIDTH`] stop; wide characters are two cells; zero-width control chars are 0).
+pub(crate) fn char_cells(c: char, at: usize) -> usize {
+    if c == '\t' {
+        TAB_WIDTH - (at % TAB_WIDTH)
+    } else {
+        UnicodeWidthChar::width(c).unwrap_or(0)
+    }
+}
+
+/// Display width (terminal cells) of the first `col` characters of `s`.
+pub(crate) fn display_width(s: &str, col: usize) -> usize {
+    let mut w = 0;
+    for c in s.chars().take(col) {
+        w += char_cells(c, w);
+    }
+    w
+}
+
+/// Character index after moving one word forward from `col` in `line`: skip the current
+/// run of non-whitespace, then the following whitespace (lands on the next word's start).
+pub(crate) fn next_word(line: &str, col: usize) -> usize {
+    let chars: Vec<char> = line.chars().collect();
+    let n = chars.len();
+    let mut i = col;
+    while i < n && !chars[i].is_whitespace() {
+        i += 1;
+    }
+    while i < n && chars[i].is_whitespace() {
+        i += 1;
+    }
+    i
+}
+
+/// Character index after moving one word backward from `col` in `line`: skip whitespace,
+/// then the preceding word (lands on that word's start).
+pub(crate) fn prev_word(line: &str, col: usize) -> usize {
+    let chars: Vec<char> = line.chars().collect();
+    let mut i = col;
+    while i > 0 && chars[i - 1].is_whitespace() {
+        i -= 1;
+    }
+    while i > 0 && !chars[i - 1].is_whitespace() {
+        i -= 1;
+    }
+    i
+}
+
+/// Rewrites a `⌘`-modified key to its `ctrl` equivalent (terminals report Super for Cmd
+/// under the kitty protocol; edtui/our bindings key off ctrl).
+pub(crate) fn super_to_ctrl(mut key: KeyEvent) -> KeyEvent {
+    if key.modifiers.contains(KeyModifiers::SUPER) {
+        key.modifiers.remove(KeyModifiers::SUPER);
+        key.modifiers.insert(KeyModifiers::CONTROL);
+    }
+    key
+}