fix(feed): widen source_ref from VARCHAR(100) to TEXT

OTX pulse names exceed 100 characters, causing a column-too-long error on
IOC feed upsert. TEXT has no length limit and matches the description column.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/resources/db/migration/V8__widen_source_ref_to_text.sql

@@ -0,0 +1 @@
+ALTER TABLE threat_ioc ALTER COLUMN source_ref TYPE TEXT;