refactor(chunk): Chunk 생성부의 aliases 리터럴 + store 컬럼 제거

kebab-chunk/* AST·md·tier2·pdf chunker 의 aliases: None 리터럴 삭제,
store-sqlite documents.rs chunks INSERT 컬럼/바인딩 + get_chunk 매핑에서
aliases 제거.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -123,8 +123,8 @@ impl kebab_core::DocumentStore for SqliteStore {
                     chunk_id, doc_id, text, heading_path_json,
                     section_label, source_spans_json, token_estimate,
                     chunker_version, policy_hash, block_ids_json, created_at,
-                    tokenized_korean_text, aliases
-                ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+                    tokenized_korean_text
+                ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
             )
             .map_err(StoreError::from)?;
         for chunk in chunks {
@@ -153,7 +153,6 @@ impl kebab_core::DocumentStore for SqliteStore {
                 block_ids,
                 now,
                 chunk.tokenized_korean_text.as_deref(),
-                chunk.aliases.as_deref(),
             ])
             .map_err(StoreError::from)?;
         }
@@ -268,7 +267,6 @@ impl kebab_core::DocumentStore for SqliteStore {
             chunker_version: kebab_core::ChunkerVersion(row.chunker_version),
             policy_hash: row.policy_hash,
             tokenized_korean_text: row.tokenized_korean_text,
-            aliases: None,
         }))
     }