feat(tui): responsive breakpoints for detail views (bd-a6yb)

Apply breakpoint-aware layout to issue_detail and mr_detail views:
- Issue detail: hide labels on Xs, hide assignees on Xs/Sm, skip milestone row on Xs
- MR detail: hide branch names and merge status on Xs/Sm
- Issue detail allocate_sections gives description 60% on wide (Lg+) vs 40% narrow
- Add responsive tests for both detail views
- Close bd-a6yb: all TUI screens now adapt to terminal width

760 lib tests pass, clippy clean.

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

@@ -20,6 +20,7 @@ use ftui::render::drawing::Draw;
 use ftui::render::frame::Frame;
 
 use crate::clock::Clock;
+use crate::layout::{classify_width, timeline_time_width};
 use crate::message::TimelineEventKind;
 use crate::state::timeline::TimelineState;
 use crate::view::common::discussion_tree::format_relative_time;
@@ -121,7 +122,9 @@ pub fn render_timeline(
     if state.events.is_empty() {
         render_empty_state(frame, state, area.x + 1, y, max_x);
     } else {
-        render_event_list(frame, state, area.x, y, area.width, list_height, clock);
+        let bp = classify_width(area.width);
+        let time_col_width = timeline_time_width(bp);
+        render_event_list(frame, state, area.x, y, area.width, list_height, clock, time_col_width);
     }
 
     // -- Hint bar --
@@ -153,6 +156,7 @@ fn render_empty_state(frame: &mut Frame<'_>, state: &TimelineState, x: u16, y: u
 // ---------------------------------------------------------------------------
 
 /// Render the scrollable list of timeline events.
+#[allow(clippy::too_many_arguments)]
 fn render_event_list(
     frame: &mut Frame<'_>,
     state: &TimelineState,
@@ -161,6 +165,7 @@ fn render_event_list(
     width: u16,
     list_height: usize,
     clock: &dyn Clock,
+    time_col_width: u16,
 ) {
     let max_x = x + width;
 
@@ -198,10 +203,9 @@ fn render_event_list(
 
         let mut cx = x + 1;
 
-        // Timestamp gutter (right-aligned in ~10 chars).
+        // Timestamp gutter (right-aligned, width varies by breakpoint).
         let time_str = format_relative_time(event.timestamp_ms, clock);
-        let time_width = 10u16;
-        let time_x = cx + time_width.saturating_sub(time_str.len() as u16);
+        let time_x = cx + time_col_width.saturating_sub(time_str.len() as u16);
         let time_cell = if is_selected {
             selected_cell
         } else {
@@ -211,8 +215,8 @@ fn render_event_list(
                 ..Cell::default()
             }
         };
-        frame.print_text_clipped(time_x, y, &time_str, time_cell, cx + time_width);
-        cx += time_width + 1;
+        frame.print_text_clipped(time_x, y, &time_str, time_cell, cx + time_col_width);
+        cx += time_col_width + 1;
 
         // Entity prefix: #42 or !99
         let prefix = match event.entity_key.kind {