feat: write to context.md by default

CONTEXT.md

@@ -0,0 +1,24 @@
+# OpenCode Development Context
+
+## Build Commands
+- Build: `go build`
+- Run: `go run main.go`
+- Test: `go test ./...`
+- Test single package: `go test ./internal/package/...`
+- Test single test: `go test ./internal/package -run TestName`
+- Verbose test: `go test -v ./...`
+- Coverage: `go test -cover ./...`
+- Lint: `go vet ./...`
+- Format: `go fmt ./...`
+- Build snapshot: `./scripts/snapshot`
+
+## Code Style
+- Use Go 1.24+ features
+- Follow standard Go formatting (gofmt)
+- Use table-driven tests with t.Parallel() when possible
+- Error handling: check errors immediately, return early
+- Naming: CamelCase for exported, camelCase for unexported
+- Imports: standard library first, then external, then internal
+- Use context.Context for cancellation and timeouts
+- Prefer interfaces for dependencies to enable testing
+- Use testify for assertions in tests