feat: add graphify plugin and documentation

- Introduced a new graphify OpenCode plugin to remind users about the knowledge graph before executing bash commands.
- Added AGENTS.md for agent guidance, including development commands, environment setup, Docker deployment, code structure, conventions, and testing instructions.
- Created opencode.json to configure the graphify plugin and superpowers.
- Updated tests to improve type safety and added missing imports in test files.
- Added .graphify_uncached.txt to track relevant files for graphify.

tests/lib/tax.test.ts

@@ -1,3 +1,5 @@
+import { describe, it, expect } from "vitest";
+
 import {
   TAX_RATES,
   calcItemAmounts,