refactor(rename): kb → kebab — binary, env vars, XDG paths, file renames

두 번째 commit. 사용자 facing surface (CLI binary, env vars, XDG paths)
+ 코드 안 single-letter token (`KB_`, `kb.sqlite`, `/kb/`, tracing
target) 일괄 rename. 그리고 3 개 file rename:

- 디자인 doc `2026-04-27-kb-final-form-design.md` →
  `2026-04-27-kebab-final-form-design.md`
- 최초 보고서 `kb_local_rust_report.md` → `kebab_local_rust_report.md`
- workspace ignore `.kbignore` → `.kebabignore`

## 변경

- `crates/kebab-cli/Cargo.toml`: `[[bin]] name = "kb"` → `"kebab"`.
- `crates/kebab-cli/src/main.rs`: `#[command(name = "kb", …)]` →
  `name = "kebab"`.
- 모든 `KB_*` env var (코드 + doc + 테스트) → `KEBAB_*`. apply_env
  prefix 매칭 + 30+ 개 setting 키 모두.
- XDG paths: `~/.config/kb` / `~/.local/share/kb` / `~/.cache/kb` /
  `~/.local/state/kb` → `~/.config/kebab` 등. config defaults +
  expand_path tests + paths.rs 의 hardcode 모두.
- SQLite filename: `kb.sqlite` → `kebab.sqlite` (`SQLITE_FILE` const
  + 테스트 hardcode 모두).
- tracing target: `target: "kb-*"` → `"kebab-*"` (10+ 곳).
- snapshot fixture: `.kbignore` → `.kebabignore` (`fixtures/source-fs/
  tree-1.snapshot.json` 갱신).

## 검증

- `cargo test --workspace -j 1` clean (linker OOM 회피 위해 직렬).
- `cargo clippy --workspace --all-targets -- -D warnings` clean.

다음 commit 에서 docs sweep.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

crates/kebab-store-sqlite/tests/common/mod.rs

@@ -37,7 +37,7 @@ impl TestEnv {
     }
 
     pub fn db_path(&self) -> PathBuf {
-        self.temp.path().join("kb.sqlite")
+        self.temp.path().join("kebab.sqlite")
     }
 
     /// Open a side-channel rusqlite connection for direct SQL inspection.

crates/kebab-store-sqlite/tests/fts.rs

@@ -335,7 +335,7 @@ fn normalize_ws(s: &str) -> String {
 /// - no `END;` after the virtual-table line
 fn extract_design_5_5_fts_block() -> String {
     let doc = include_str!(
-        "../../../docs/superpowers/specs/2026-04-27-kb-final-form-design.md"
+        "../../../docs/superpowers/specs/2026-04-27-kebab-final-form-design.md"
     );
     let heading_idx = doc
         .find("### 5.5 Chunks + FTS5")
@@ -437,7 +437,7 @@ fn fts_v002_matches_design_section_5_5_verbatim() {
 // ── 6. WAL cleanup: drop store before tempdir reaps WAL/SHM ──────────
 
 /// Mirror the P1-6 pattern: opening + migrating + dropping the store
-/// must not strand `kb.sqlite-wal`/`-shm` files such that the tempdir
+/// must not strand `kebab.sqlite-wal`/`-shm` files such that the tempdir
 /// can't be cleaned up. After dropping the store + side-channel conn,
 /// the WAL/SHM siblings must either not exist or be removable — if a
 /// stray handle were holding them open, on Windows the remove would