refactor(cli): adopt flex-width rendering, remove data-layer truncation

Replace hardcoded truncation widths across CLI commands with
render::flex_width() calls that adapt to terminal size. Remove
server-side truncate_to_chars() in timeline collect/seed stages so
full text is preserved through the pipeline — truncation now happens
only at the presentation layer where terminal width is known.

Affected commands: explain, file-history, list (issues/mrs/notes),
me, timeline, who (active/expert/workload).

src/timeline/timeline_collect_tests.rs

@@ -553,9 +553,10 @@ fn test_collect_discussion_thread_body_truncation() {
         .unwrap();
 
     if let TimelineEventType::DiscussionThread { notes, .. } = &thread.event_type {
-        assert!(
-            notes[0].body.chars().count() <= crate::timeline::THREAD_NOTE_MAX_CHARS,
-            "Body should be truncated to THREAD_NOTE_MAX_CHARS"
+        assert_eq!(
+            notes[0].body.chars().count(),
+            10_000,
+            "Body should preserve full text without truncation"
         );
     } else {
         panic!("Expected DiscussionThread");