refactor(tui): deduplicate cursor_cell_offset into text_width module

Four view modules (search, command_palette, file_history, trace) each had
their own copy of cursor_cell_offset / text_cell_width for converting a
byte-offset cursor position to a display-column offset. Phase 5 introduced
a proper text_width module with these functions; this commit removes the
duplicates and rewires all call sites to use crate::text_width.

- search.rs: removed local text_cell_width + cursor_cell_offset definitions
- command_palette.rs: removed local cursor_cell_offset definition
- file_history.rs: replaced inline chars().count() cursor calc with import
- trace.rs: replaced inline chars().count() cursor calc with import

crates/lore-tui/src/view/search.rs

@@ -18,24 +18,11 @@
 use ftui::core::geometry::Rect;
 use ftui::render::cell::Cell;
 use ftui::render::drawing::Draw;
-
-/// Count display-width columns for a string (char count, not byte count).
-fn text_cell_width(text: &str) -> u16 {
-    text.chars().count().min(u16::MAX as usize) as u16
-}
-
-/// Convert a byte-offset cursor position to a display-column offset.
-fn cursor_cell_offset(query: &str, cursor: usize) -> u16 {
-    let mut idx = cursor.min(query.len());
-    while idx > 0 && !query.is_char_boundary(idx) {
-        idx -= 1;
-    }
-    text_cell_width(&query[..idx])
-}
 use ftui::render::frame::Frame;
 
 use crate::message::EntityKind;
 use crate::state::search::SearchState;
+use crate::text_width::cursor_cell_offset;
 
 use super::{ACCENT, BG_SURFACE, BORDER, TEXT, TEXT_MUTED};