feat(05-01): migrate findings schema with verify_* columns

- schema.sql: new findings columns verified, verify_status, verify_http_code, verify_metadata_json
- db.go: migrateFindingsVerifyColumns runs on Open() for legacy DBs using PRAGMA table_info + ALTER TABLE
- findings.go: Finding struct gains Verified/VerifyStatus/VerifyHTTPCode/VerifyMetadata
- SaveFinding serializes verify metadata as JSON (NULL when nil)
- ListFindings round-trips all verify fields

pkg/storage/schema.sql

@@ -11,16 +11,20 @@ CREATE TABLE IF NOT EXISTS scans (
 );
 
 CREATE TABLE IF NOT EXISTS findings (
-    id            INTEGER PRIMARY KEY AUTOINCREMENT,
-    scan_id       INTEGER REFERENCES scans(id),
-    provider_name TEXT NOT NULL,
-    key_value     BLOB NOT NULL,
-    key_masked    TEXT NOT NULL,
-    confidence    TEXT NOT NULL,
-    source_path   TEXT,
-    source_type   TEXT,
-    line_number   INTEGER,
-    created_at    DATETIME DEFAULT CURRENT_TIMESTAMP
+    id                   INTEGER PRIMARY KEY AUTOINCREMENT,
+    scan_id              INTEGER REFERENCES scans(id),
+    provider_name        TEXT NOT NULL,
+    key_value            BLOB NOT NULL,
+    key_masked           TEXT NOT NULL,
+    confidence           TEXT NOT NULL,
+    source_path          TEXT,
+    source_type          TEXT,
+    line_number          INTEGER,
+    verified             INTEGER NOT NULL DEFAULT 0,
+    verify_status        TEXT NOT NULL DEFAULT '',
+    verify_http_code     INTEGER NOT NULL DEFAULT 0,
+    verify_metadata_json TEXT,
+    created_at           DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
 CREATE TABLE IF NOT EXISTS settings (