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/search.rs

@@ -7,7 +7,7 @@ use kebab_core::{
     RetrievalDetail, SearchHit, SearchMode, WorkspacePath,
 };
 use kebab_tui::{
-    App, KeyOutcome, Pane, SearchState, SearchWorkerMessage, build_jump_command,
+    App, KeyOutcome, Mode, Pane, SearchState, SearchWorkerMessage, build_jump_command,
     handle_key_search, poll_search_worker, render_search, search_debounce_due,
 };
 use ratatui::Terminal;
@@ -572,3 +572,56 @@ fn hangul_typing_in_search_input_advances_cursor_by_two_per_char() {
     assert_eq!(app.search.as_ref().unwrap().input.as_str(), "한");
     assert_eq!(app.search.as_ref().unwrap().input.cursor_col(), 2);
 }
+
+/// p9-fb-21: chunk-inspect was rebound from `i` to `o` so `i`
+/// could become the universal Normal→Insert toggle. Pin the new
+/// `o` key — Normal mode + at least one hit + selected → SwitchPane(Inspect).
+#[test]
+fn o_in_normal_with_hits_enters_inspect() {
+    let mut app = fresh_app();
+    app.focus = Pane::Search;
+    app.mode = Mode::Normal;
+    let s = app.search.as_mut().unwrap();
+    s.hits = vec![make_hit(
+        1,
+        "a.md",
+        "snippet",
+        line_citation("a.md", 1),
+    )];
+    s.selected_hit = 0;
+    let outcome = kebab_tui::handle_key_search(
+        &mut app,
+        KeyEvent::new(KeyCode::Char('o'), KeyModifiers::NONE),
+    );
+    assert_eq!(outcome, KeyOutcome::SwitchPane(Pane::Inspect));
+}
+
+/// p9-fb-21: `o` with empty hits is a no-op (Continue) — do not
+/// enter Inspect with no target.
+#[test]
+fn o_in_normal_with_empty_hits_is_continue() {
+    let mut app = fresh_app();
+    app.focus = Pane::Search;
+    app.mode = Mode::Normal;
+    let outcome = kebab_tui::handle_key_search(
+        &mut app,
+        KeyEvent::new(KeyCode::Char('o'), KeyModifiers::NONE),
+    );
+    assert_eq!(outcome, KeyOutcome::Continue);
+}
+
+/// p9-fb-21: in Insert mode, `o` types as a regular char (the
+/// chunk-inspect intercept only fires in Normal). Pin so a future
+/// regression that drops the `is_normal` guard would fail this.
+#[test]
+fn o_in_insert_types_into_input() {
+    let mut app = fresh_app();
+    app.focus = Pane::Search;
+    app.mode = Mode::Insert;
+    let outcome = kebab_tui::handle_key_search(
+        &mut app,
+        KeyEvent::new(KeyCode::Char('o'), KeyModifiers::NONE),
+    );
+    assert_eq!(outcome, KeyOutcome::Continue);
+    assert_eq!(app.search.as_ref().unwrap().input.as_str(), "o");
+}