fix: keyword search for OCR text

- Fix OCR confidence threshold: 0.5 → 0.2
- Fix fetch_ocr_texts frame calculation (use start_frame from DB)
- Fix text_match filter to use text_content instead of summary
- Process all merged results (not just top 30) to include keyword results
- Add logging for keyword search debugging

Fixes issue where OCR text like 'AUDIO MONITORING' and 'thunderbolt'
could not be found via keyword search.

src/core/chunk/rule1_ingest.rs

@@ -7,7 +7,7 @@ use sqlx::{PgPool, Row};
 use std::collections::BTreeMap;
 use tracing::{info, warn};
 
-const OCR_CONFIDENCE_THRESHOLD: f64 = 0.5;
+const OCR_CONFIDENCE_THRESHOLD: f64 = 0.2;
 
 pub async fn execute_rule1(db: &PostgresDb, file_uuid: &str, fps: f64) -> Result<usize> {
     let pool = db.pool();
@@ -219,11 +219,10 @@ async fn fetch_ocr_texts(
 
     let mut map: BTreeMap<i64, Vec<String>> = BTreeMap::new();
     for row in rows {
-        let start_time: f64 = row.try_get("start_time").unwrap_or(0.0);
+        let start_frame: i64 = row.try_get("start_frame").unwrap_or(0);
         let end_time_raw: Option<f64> = row.try_get("end_time").ok();
         let data: Value = row.try_get("data").unwrap_or(Value::Null);
 
-        let start_frame = (start_time * fps) as i64;
         let end_frame = end_time_raw
             .filter(|t| *t > 0.0)
             .map(|t| (t * fps) as i64)