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/test/fixture/db.ts

@@ -0,0 +1,11 @@
+import { rm } from "fs/promises"
+import { Instance } from "../../src/project/instance"
+import { Database } from "../../src/storage/db"
+
+export async function resetDatabase() {
+  await Instance.disposeAll().catch(() => undefined)
+  Database.close()
+  await rm(Database.Path, { force: true }).catch(() => undefined)
+  await rm(`${Database.Path}-wal`, { force: true }).catch(() => undefined)
+  await rm(`${Database.Path}-shm`, { force: true }).catch(() => undefined)
+}