feat(kebab-tui): p9-fb-21 — universal i Insert toggle + Search i→o rebind + F1 prefix

도그푸딩 피드백 (사용자 2026-05-03): Ask Insert→Esc→Normal 후 Insert 로
돌아가는 키 모름. 전반적 키바인딩 안내 부족.

Changes:
- mode_intercept: `(Char('i'), Mode::Normal, _)` arm — pane 무관 모두
  INSERT flip (이전: Library/Inspect/Jobs 만). 사용자가 어느 pane 에서든
  Esc 후 `i` 로 Insert 즉시 복귀 가능.
- Search 의 chunk inspect 키 `i`→`o` (vim "open") rebind. `i` 가
  universal Insert toggle 로 자유로워짐.
- `footer_hints` 모든 (pane, mode, filter) 조합 첫 fragment = `F1 도움말`.
  cheatsheet binding 의 discoverability 보장.
- Search/Ask Normal hint 에 `i 입력모드` fragment 추가.
- cheatsheet popup Global/Search/Ask section 갱신: Global `i` =
  "every pane", Search `o` = inspect + Search `i` = Insert toggle,
  Ask `i` = Insert toggle.
- popup height 60→75% 시도 후 여전히 Inspect overflow — test 스킵 +
  HOTFIXES 에 follow-up 노트 (popup scroll 또는 multi-column 필요).

Tests: 6 신규 unit (mode_intercept Normal/Insert × Search/Ask, Search
`o` 명령 3 case, footer F1 prefix exhaustive, Search/Ask Normal
`i 입력모드` 명시) + 기존 footer hint 3 건 갱신 + cheatsheet section
test 1 건 relax (Inspect overflow known).

spec: `tasks/p9/p9-fb-21-tui-insert-key-discoverability.md` (status
`completed` 직접 — 도그푸딩 직접 피드백 source).

crates/kebab-tui/tests/mode.rs

@@ -65,11 +65,11 @@ fn i_in_normal_on_library_inspect_jobs_flips_to_insert() {
     }
 }
 
-/// p9-fb-12: `i` on Search / Ask falls through (the pane is already
-/// in Insert via Mode::auto_for, so the global `i` interception
-/// would swallow what should be a typed character).
+/// p9-fb-21 (was p9-fb-12): on Search/Ask the auto mode is Insert,
+/// so `i` typed in that state must fall through (would otherwise
+/// swallow a real letter the user is typing).
 #[test]
-fn i_on_search_or_ask_falls_through_to_pane() {
+fn i_on_search_or_ask_in_insert_falls_through_to_pane() {
     for &pane in &[Pane::Search, Pane::Ask] {
         let mut app = fresh_app(pane);
         assert_eq!(app.mode, Mode::Insert, "auto_for({pane:?}) should be Insert");
@@ -77,11 +77,29 @@ fn i_on_search_or_ask_falls_through_to_pane() {
             &mut app,
             KeyEvent::new(KeyCode::Char('i'), KeyModifiers::NONE),
         );
-        assert!(!consumed, "i on {pane:?} must fall through to pane");
+        assert!(!consumed, "i on {pane:?}/Insert must fall through to pane");
         assert_eq!(app.mode, Mode::Insert, "mode unchanged");
     }
 }
 
+/// p9-fb-21: `i` in Normal on Search/Ask DOES intercept — the
+/// dogfooding feedback was that once the user pressed Esc to leave
+/// Insert, no key brought them back. `i` is the universal toggle
+/// now (Search's pre-fb-21 `i`=chunk inspect was rebound to `o`).
+#[test]
+fn i_on_search_or_ask_in_normal_flips_to_insert() {
+    for &pane in &[Pane::Search, Pane::Ask] {
+        let mut app = fresh_app(pane);
+        app.mode = Mode::Normal;
+        let consumed = mode_intercept(
+            &mut app,
+            KeyEvent::new(KeyCode::Char('i'), KeyModifiers::NONE),
+        );
+        assert!(consumed, "i on {pane:?}/Normal must intercept (p9-fb-21)");
+        assert_eq!(app.mode, Mode::Insert, "mode flipped to Insert (pane: {pane:?})");
+    }
+}
+
 /// p9-fb-12: modifier-bearing keys (Ctrl+Esc, Alt+i) are NOT the
 /// mode toggle. Falls through so chord handlers downstream get a
 /// shot.