fix(fb-35): address PR #126 round 2 review

- wire schema: relax effective_end.minimum 1 → 0 + expand
  description to cover line-clamp + out-of-range sentinel
  (panic-fix R1 emits Some(0) when line_start=1 and range is
  beyond doc end — schema must accept it)
- tests: tighten first-chunk-target boundary test to assert ≤ 2
  total neighbors (3-chunk doc, N=2). Strict "first chunk →
  context_before empty" not assertable until chunks.ordinal
  column lands (R1 #9 architectural caveat)
- store: trim contradiction in list_chunk_ids_for_doc warning
  comment — drop "good enough for sequentially chunked
  markdown" phrase that conflicts with "hash sort dominates"
  paragraph above

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

crates/kebab-store-sqlite/src/documents.rs

@@ -389,10 +389,11 @@ impl SqliteStore {
     ///
     /// Real fix is a `chunks.ordinal` column (V007 migration) or sort
     /// by `chunks.source_spans_json[0]` start offset. Tracked as
-    /// follow-up; current behavior is good enough for sequentially
-    /// chunked markdown where created_at uniqueness varies, but PDFs
-    /// (page-aligned chunks) and large docs may surprise the agent.
-    /// See `tasks/HOTFIXES.md` if/when this is escalated.
+    /// follow-up. Until then `--context` neighbors are best-effort —
+    /// they may or may not align with document position depending on
+    /// whether `chunk_id` hash order happens to match insertion order
+    /// for that particular doc. Large markdown / PDF (page-aligned
+    /// chunks) likely re-orders. See `tasks/HOTFIXES.md` if escalated.
     pub fn list_chunk_ids_for_doc(
         &self,
         doc_id: &kebab_core::DocumentId,