add agent rules

.opencode/rules/linting.md

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+# Linting
+
+## Command
+
+- Run `pnpm lint` (Prettier check + ESLint) before finishing any work.
+- If `pnpm lint` reports errors, fix them and re-run until clean.
+- Never leave the repo in a state where `pnpm lint` fails.
+
+## ESLint
+
+- The flat config in `eslint.config.js` is the source of truth for enabled rules. Read it before making lint-related assumptions.
+- `.svelte` files are handled by `eslint-plugin-svelte` with the TypeScript parser.
+- `eslint.config.js` respects `.gitignore` — don't lint `build/`, `.svelte-kit/`, or `node_modules/`.
+- Prefer fixing the root cause over suppressing: avoid `eslint-disable` comments unless truly necessary, and never disable an entire file.
+- Run `pnpm lint` for the whole project after edits that touch Svelte, TypeScript, or configuration files.