feat(kebab-tui): P9-4 Inspect pane — doc/chunk detail with collapsible sections

Library Enter / Search 'i' 가 Inspect 진입. Doc 또는 Chunk 단일 view 로
metadata / provenance / blocks (doc) 또는 spans / text / embeddings (chunk)
6 section 을 collapsible 로 표시. Esc/q 로 originating pane 으로 복귀.

핵심:
- InspectTarget enum (`Doc(DocumentId) | Chunk(ChunkId)`).
- InspectState 본체 (`app.rs`) — target / doc / chunk / collapsed
  HashSet / scroll / return_to / needs_fetch / loading.
- `src/inspect.rs`:
  - `render_inspect` — target 종류별 render_doc / render_chunk 분기,
    section header 가 collapse marker (▾/▸) 표시. metadata.user JSON
    pretty-printed.
  - `handle_key_inspect`: j/k / Down/Up scroll. PageDown/PageUp 10 row.
    c = toggle all sections (v1 simplification). Esc/q = SwitchPane(return_to).
  - `enter_inspect(state, target, return_to)` helper — Library 와 Search
    공통 entry point.
  - run-loop hook `refresh_inspect` — needs_fetch 면 lazy
    inspect_doc_with_config / inspect_chunk_with_config.
- run.rs: Pane::Inspect arm 이 handle_key_inspect + render_inspect.
  Idle tick 마다 refresh_inspect. SwitchPane(Inspect) lazy init.
- Library: Enter 가 enter_inspect(Doc(selected)) 호출 후 SwitchPane.
- Search: 'i' (plain modifier) 가 enter_inspect(Chunk(selected_hit))
  호출 후 SwitchPane. typing 'i' (\"instance\") 와 충돌 가드.

테스트 12개 (`tests/inspect.rs`, TestBackend) — Esc 가 return_to 사용
/ q 도 동작 / j/k scroll bounds / PgUp PgDn ±10 / c 일괄 toggle / no
target hint / loading / doc view header+metadata+provenance+blocks /
collapse hides body / chunk view text+block_ids / no slot →
SwitchPane(Library) / enter_inspect helper sets fields.

Spec deviation (HOTFIXES `2026-05-02 P9-4`):
- `render_inspect<B: Backend>` generic 제거 (P9-1/2/3 와 동일).
- Search `i` 키 추가 (P9-2 spec 에 없었음, P9-4 retroactive 추가).
- `c` 일괄 collapse — spec 의 \"focus 기반 selective collapse\" 는 P+.

Docs (sync rule):
- README: TUI 행 \"4 패널\" + Quick start 코멘트.
- HANDOFF: 한 줄 요약 + Phase status (P9 3/5 → 4/5) + deviation 한 줄.
- HOTFIXES: P9-4 entry.
- tasks/p9/p9-4 status: completed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tasks/HOTFIXES.md

@@ -14,6 +14,29 @@ historical contract that was implemented; this file accumulates the
 deltas so phase 5+ readers can find the live behavior without diffing
 git history.
 
+## 2026-05-02 — P9-4 TUI Inspect: render_inspect generic + Search `i` entry + collapse simplification
+
+**Discovered**: P9-4 implementation start.
+
+**Symptom 1 (cosmetic)**: Same shape as P9-1/2/3 — `tasks/p9/p9-4-tui-inspect.md` § Public surface declares `render_inspect<B: ratatui::backend::Backend>(...)`. ratatui 0.28's `Frame` is backend-agnostic; the generic is unused.
+
+**Symptom 2 (load-bearing)**: Spec § Behavior contract names `Search pressing 'i' (new key on Search pane) passes Chunk(selected_hit.chunk_id)` — but P9-2 (already merged) didn't include `i`. The Inspect entry from Search has to be wired retroactively.
+
+**Symptom 3 (simplification)**: Spec § Behavior contract section on collapse: "focus is implicit by current scroll position; v1 may simplify by toggling all sections". Implementation takes the v1 path — `c` toggles all six sections (metadata / provenance / blocks / spans / text / embeddings) at once. Per-section focus is a P+ enhancement.
+
+**Fix**:
+- `render_inspect(f: &mut Frame, area: Rect, state: &App)` — no generic.
+- New helper `kebab_tui::enter_inspect(state, target, return_to)` lifted out of pane handlers so both Library `Enter` and Search `i` use the same code path.
+- Search pane gains `i` keybinding (pre-pass like `g`, plain modifier only — typing `i` in queries still reaches input). Esc returns the user to the originating pane stored in `return_to`.
+- `InspectState.collapsed: HashSet<&'static str>` records collapsed section names. `c` flips all-collapsed ↔ all-expanded based on whether any are currently collapsed.
+- `q` joins `Esc` as the back key (Inspect is the only read-only terminal pane in v1, so `q` is unambiguous).
+
+**Trust note**: Embedding inspection is intentionally left as "(not loaded — out of v1 scope)" per spec § Out of scope. The full embedding-record fetch would require an extra facade method (`kebab-app::inspect_embedding`) that is not in the P5/P6/P7 facade surface. P+ task.
+
+**Amends**:
+- tasks/p9/p9-4-tui-inspect.md (`render_inspect` non-generic; collapse simplification; entry helper).
+- tasks/p9/p9-2-tui-search.md (Search pane gains `i` for chunk inspect — was not in original p9-2 spec).
+
 ## 2026-05-02 — P9-3 TUI Ask: render_ask generic + command-vs-insert key disambiguation
 
 **Discovered**: P9-3 implementation start.