refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

packages/tfcode/script/check-migrations.ts

@@ -0,0 +1,16 @@
+#!/usr/bin/env bun
+
+import { $ } from "bun"
+
+// drizzle-kit check compares schema to migrations, exits non-zero if drift
+const result = await $`bun drizzle-kit check`.quiet().nothrow()
+
+if (result.exitCode !== 0) {
+  console.error("Schema has changes not captured in migrations!")
+  console.error("Run: bun drizzle-kit generate")
+  console.error("")
+  console.error(result.stderr.toString())
+  process.exit(1)
+}
+
+console.log("Migrations are up to date")