fix: bump cache schema version to force Parquet rebuild after migration

Existing v2 caches may have been built before the schema migration
added phone_number to the participants table, resulting in Parquet
files without the column. Bumping to v3 ensures build-cache detects
the mismatch and triggers a full rebuild automatically.

Author: eddowding

cmd/msgvault/cmd/build_cache.go

@@ -31,7 +31,7 @@ var buildCacheMu sync.Mutex
 // columns are added/removed/renamed in the COPY queries below so that
 // incremental builds automatically trigger a full rebuild instead of
 // producing Parquet files with mismatched schemas.
-const cacheSchemaVersion = 2 // v2: added sender_id, message_type, attachment_count, phone_number, title
+const cacheSchemaVersion = 3 // v3: schema migration adds phone_number etc. to existing DBs; force Parquet rebuild
 
 // syncState tracks the last exported message ID for incremental updates.
 type syncState struct {