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_seed_tests.rs

@@ -288,7 +288,7 @@ fn test_seed_evidence_snippet_truncated() {
         if let TimelineEventType::NoteEvidence { snippet, .. } =
             &result.evidence_notes[0].event_type
         {
-            assert!(snippet.chars().count() <= 200);
+            assert_eq!(snippet.chars().count(), 500, "snippet should preserve full body text");
         } else {
             panic!("Expected NoteEvidence");
         }