feat(db): Add migration 010 for chunk config tracking columns

Add chunk_max_bytes and chunk_count columns to embedding_metadata to
support config drift detection and adaptive dedup sizing. Includes a
partial index on sentinel rows (chunk_index=0) to accelerate the drift
detection and max-chunk queries.

Also exports LATEST_SCHEMA_VERSION as a public constant derived from
the MIGRATIONS array length, replacing the previously hardcoded magic
number in the health check.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/core/db.rs

@@ -10,6 +10,10 @@ use tracing::{debug, info};
 
 use super::error::{LoreError, Result};
 
+/// Latest schema version, derived from the embedded migrations count.
+/// Used by the health check to verify databases are up-to-date.
+pub const LATEST_SCHEMA_VERSION: i32 = MIGRATIONS.len() as i32;
+
 /// Embedded migrations - compiled into the binary.
 const MIGRATIONS: &[(&str, &str)] = &[
     ("001", include_str!("../../migrations/001_initial.sql")),
@@ -39,6 +43,10 @@ const MIGRATIONS: &[(&str, &str)] = &[
         "009",
         include_str!("../../migrations/009_embeddings.sql"),
     ),
+    (
+        "010",
+        include_str!("../../migrations/010_chunk_config.sql"),
+    ),
 ];
 
 /// Create a database connection with production-grade pragmas.