feat(store): V008 pdf_ocr_events migration + record/prune API (Enhancement 2)

Add migrations/V008__pdf_ocr_events.sql with the events table + 3
indices (doc_id, run_id, ts). SqliteStore gains two pub fn:
record_pdf_ocr_event (insert one OCR sample) and prune_pdf_ocr_events
(delete rows older than retention_days; returns the affected row
count). Both follow the existing Mutex<Connection> lock pattern.

Wiring into ingest path lands in the next commit.

Closure r1 F2: explicit lock acquisition in both methods.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/kebab-store-sqlite/tests/pdf_ocr_events_insert_smoke.rs

@@ -0,0 +1,89 @@
+//! Smoke tests for V008 pdf_ocr_events migration + record/prune API (Enhancement 2).
+//! AC-2, AC-3, AC-8.
+
+mod common;
+
+use kebab_store_sqlite::SqliteStore;
+use rusqlite::OptionalExtension;
+
+fn open_migrated() -> (common::TestEnv, SqliteStore) {
+    let env = common::TestEnv::new();
+    let store = SqliteStore::open(&env.config()).expect("open");
+    store.run_migrations().expect("run migrations");
+    (env, store)
+}
+
+/// AC-2: V008 migration creates the pdf_ocr_events table.
+#[test]
+fn v008_pdf_ocr_events_table_exists() {
+    let (env, _store) = open_migrated();
+    let name: Option<String> = env.with_conn(|c| {
+        c.query_row(
+            "SELECT name FROM sqlite_master WHERE type='table' AND name='pdf_ocr_events'",
+            [],
+            |r| r.get(0),
+        )
+        .optional()
+    });
+    assert_eq!(name.as_deref(), Some("pdf_ocr_events"), "pdf_ocr_events table must exist after V008");
+}
+
+/// AC-8: insert 2 rows with different timestamps; prune with retention_days=0
+/// (cutoff = now) → the old row is deleted, count returns 1.
+#[test]
+fn record_and_prune_pdf_ocr_event() {
+    let (_env, store) = open_migrated();
+
+    // Row 1: very old timestamp (1970)
+    store
+        .record_pdf_ocr_event(
+            "run-old",
+            "1970-01-01T00:00:00Z",
+            Some("doc-old"),
+            "path/old.pdf",
+            1,
+            Some(12345),
+            Some(100),
+            Some(80),
+            250,
+            42,
+            true,
+            None,
+            "qwen2.5vl",
+        )
+        .expect("insert old row");
+
+    // Row 2: future timestamp (far future, so it survives prune)
+    store
+        .record_pdf_ocr_event(
+            "run-new",
+            "2099-01-01T00:00:00Z",
+            Some("doc-new"),
+            "path/new.pdf",
+            1,
+            None,
+            None,
+            None,
+            180,
+            30,
+            true,
+            None,
+            "qwen2.5vl",
+        )
+        .expect("insert future row");
+
+    // prune with retention_days=0 → cutoff=now → deletes any row with ts < now.
+    // The 1970 row should be deleted; the 2099 row survives.
+    let pruned = store
+        .prune_pdf_ocr_events(0)
+        .expect("prune");
+    assert_eq!(pruned, 1, "should have deleted exactly 1 old row");
+
+    // Verify only the future row remains
+    let count: i64 = {
+        let conn = store.read_conn();
+        conn.query_row("SELECT COUNT(*) FROM pdf_ocr_events", [], |r| r.get(0))
+            .expect("count")
+    };
+    assert_eq!(count, 1, "exactly 1 row should survive after prune");
+}