Two issues surfaced during the post-P3-5 manual smoke test against a
six-document workspace:

1. --config flag was silently ignored. kb-cli read cli.config only
   while building SourceScope inside the Ingest arm, then called
   kb_app::ingest(scope, summary_only) which internally re-loads
   Config::load(None) — falling back to ~/.config/kb/config.toml
   regardless of what the user passed. Same pattern in search,
   list, inspect, doctor. Users had to rely on KB_* env vars to
   point at a non-default config.

2. Search output collapsed RRF hybrid scores to "0.02" because
   `{:.2}` truncated the (0, 0.033]-bounded fused score, and
   chunks from the same document showed up as identical lines
   ("3. 0.02  arch/rag-architecture.md") since heading_path was
   never printed.

Fix:

- kb-app: doctor/ingest/search/list/inspect already had
  *_with_config(Config, ...) seams introduced for integration tests
  (#[doc(hidden)] pub). Repurpose them as the official "config-explicit"
  API — kb-cli now builds the Config once via
  Config::load(cli.config.as_deref()) at the top of every subcommand
  and threads it into the *_with_config variant. Module doc-comment
  updated to reflect three callers (CLI --config, integration tests,
  TUI session) instead of "test-only seam".
- kb-app: doctor() rewritten as doctor_with_config_path(Option<&Path>)
  that respects an explicit path. config_loaded probe now reports the
  actual path checked, returning a clear hard error if --config points
  at a non-existent or malformed file (defaults would silently mask
  user intent). data_dir_writable resolves storage.data_dir from the
  loaded config (with env overrides applied via Config::apply_env) so
  --config users see their custom paths reflected. Original doctor()
  signature kept as a None-passing wrapper.
- kb-cli: ingest/search/list/inspect/doctor each call the
  *_with_config* companion. Search printer switches to {:.4} score
  formatting (RRF hybrid range bounded by ~2/k_rrf ≈ 0.033 at k_rrf=60
  default) and appends `> head1 / head2` when heading_path is non-
  empty so chunks from the same document are visually distinguishable.

Verified manually:
- `kb --config /tmp/kb-smoke/config.toml doctor` reports the
  custom config path + custom data_dir, not the XDG defaults.
- `kb --config /tmp/kb-smoke/config.toml search "..." --mode hybrid`
  returns hits with distinct 4-digit scores and heading paths
  ("rust/ownership.md > Rust 소유권 모델 / Borrow checker").

Workspace 269 passed / 24 ignored / 0 failed; cargo clippy
--workspace --all-targets -- -D warnings clean.

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

@@ -149,3 +157,2 @@
 
-/// Test-only seam — kb-cli must call the public free function
-/// ([`ingest`]), not this. See module docs.
+/// Config-explicit variant — bypasses [`load_config`] when the

@@ -840,2 +877,4 @@
+        None => kb_config::Config::xdg_data_dir(),
+    };
     let writable = (|| -> anyhow::Result<()> {
         std::fs::create_dir_all(&data_dir)?;

@@ -289,2 +293,3 @@
                 for h in &hits {
-                    println!("{:>2}. {:.2}  {}", h.rank, h.retrieval.fusion_score, h.doc_path.0);
+                    // Show 4-digit score so RRF fused scores (bounded
+                    // ~0–0.033 for k_rrf=60) don't all collapse to "0.02".