Fix Build and test CI failures from CSharpDB integer overflow in index schema

[Copilot]

The Build and test workflow was failing because index writes/read predicates were coercing large values (UTC ticks, trigram codes, hashed token IDs) into INTEGER, which overflowed under current CSharpDB type handling. This updates the index schema to use 64-bit storage where required and forces stale schema rebuilds.

• Schema correction for large numeric fields

  • Bumped IndexDatabase.CurrentSchemaVersion from 25 to 26 to trigger rebuild of incompatible local index DBs.
  • Changed affected columns from INTEGER to BIGINT in index DDL:
    • time/tick fields (*_utc_ticks)
    • file_trigrams.trigram_code
    • file_metadata_tokens.id (hash-derived, 63-bit range)

• Regression coverage

  • Added CurrentSchemaStoresUtcTicksAsBigInt to ensure current schema accepts and matches large tick values in persisted rows.

internal const string CurrentSchemaVersion = "26";

await db.ExecuteAsync(
    "CREATE TABLE IF NOT EXISTS file_trigrams (root_id INTEGER, trigram_code BIGINT, file_id INTEGER)", cancellationToken);

await db.ExecuteAsync(
    "CREATE TABLE IF NOT EXISTS file_metadata_tokens (id BIGINT PRIMARY KEY, root_id INTEGER, file_id INTEGER, token TEXT)", cancellationToken);