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-source-fs/src/connector.rs

@@ -74,13 +74,13 @@ impl SourceConnector for FsSourceConnector {
             scope.root.clone()
         };
 
-        // Union: config.workspace.exclude ∪ scope.exclude ∪ .kbignore.
-        // Per §6.2 the union of `.kbignore` and `config.workspace.exclude`
+        // Union: config.workspace.exclude ∪ scope.exclude ∪ .kebabignore.
+        // Per §6.2 the union of `.kebabignore` and `config.workspace.exclude`
         // is the filter set. `scope.exclude` is added on top so a caller
         // can layer a per-call narrowing.
         let mut excludes = self.default_exclude.clone();
         excludes.extend(scope.exclude.iter().cloned());
-        // .kbignore is re-read on every scan() so users can edit it without
+        // .kebabignore is re-read on every scan() so users can edit it without
         // restarting any long-running process.
         let kbignore = read_kbignore(&root)?;
 
@@ -243,7 +243,7 @@ mod tests {
     fn scan_filters_by_kbignore() {
         let dir = tempfile::tempdir().unwrap();
         let root = dir.path();
-        std::fs::write(root.join(".kbignore"), "*.tmp\n").unwrap();
+        std::fs::write(root.join(".kebabignore"), "*.tmp\n").unwrap();
         std::fs::write(root.join("a.md"), b"x").unwrap();
         std::fs::write(root.join("b.tmp"), b"x").unwrap();
 
@@ -252,14 +252,14 @@ mod tests {
                 .unwrap();
         let v = conn.scan(&SourceScope::default()).unwrap();
         let names: Vec<_> = v.iter().map(|a| a.workspace_path.0.clone()).collect();
-        // Decision: `.kbignore` itself IS emitted as a RawAsset (MediaType::Other("")).
+        // Decision: `.kebabignore` itself IS emitted as a RawAsset (MediaType::Other("")).
         // Rationale: a config file that affects ingest is itself part of the
         // workspace contents; the markdown extractor (P1-2) will reject Other("")
-        // on its own. If we ever decide to omit `.kbignore` from the asset list,
+        // on its own. If we ever decide to omit `.kebabignore` from the asset list,
         // this test will catch it.
         assert!(
-            names.contains(&".kbignore".to_string()),
-            ".kbignore must be emitted as an asset; got: {names:?}"
+            names.contains(&".kebabignore".to_string()),
+            ".kebabignore must be emitted as an asset; got: {names:?}"
         );
         assert!(names.contains(&"a.md".to_string()));
         assert!(!names.contains(&"b.tmp".to_string()));
@@ -285,7 +285,7 @@ mod tests {
     fn scan_unions_config_exclude_and_kbignore() {
         let dir = tempfile::tempdir().unwrap();
         let root = dir.path();
-        std::fs::write(root.join(".kbignore"), "*.tmp\n").unwrap();
+        std::fs::write(root.join(".kebabignore"), "*.tmp\n").unwrap();
         std::fs::write(root.join("a.md"), b"x").unwrap();
         std::fs::write(root.join("b.tmp"), b"x").unwrap();
         std::fs::write(root.join("c.log"), b"x").unwrap();