fix(wrangler): replace placeholder database_id for D1 FTS binding (#88)

Refs #87

PR #86 で導入した D1 binding の database_id placeholder を
実際に作成済みの D1 database (github-rag-fts, APAC region) の ID に差替え。
これで Cloudflare Workers Builds が placeholder で落ちる状態を解消する。

The D1 migration 0001_fts5_init.sql has already been applied to the remote
database via `wrangler d1 execute --file` (since the multi-statement BEGIN...END
triggers trip up wrangler's migration splitter). Migration state is recorded
in the d1_migrations tracking table.

Author: liplus-lin-lay

wrangler.toml

@@ -31,7 +31,7 @@ index_name = "github-rag-issues"
 [[d1_databases]]
 binding = "DB_FTS"
 database_name = "github-rag-fts"
-database_id = "REPLACE_WITH_D1_DATABASE_ID"
+database_id = "5e18ffa8-584c-452e-b906-2cf71120c7ad"
 migrations_dir = "migrations"
 
 # Workers AI binding for embedding generation (BGE-M3)