chore: sub-store Go 重写项目初始化

internal/database/migrations/0003_source_cache.sql

@@ -0,0 +1,11 @@
+-- +goose Up
+CREATE TABLE IF NOT EXISTS source_cache (
+  cache_key  TEXT PRIMARY KEY,
+  content    TEXT NOT NULL,
+  metadata   TEXT NOT NULL DEFAULT '{}',
+  cached_at  INTEGER NOT NULL,
+  ttl        INTEGER NOT NULL DEFAULT 300
+);
+
+CREATE INDEX IF NOT EXISTS idx_source_cache_expiry
+ON source_cache(cached_at + ttl);