docs: add coding conventions for agentic coding

CONVENTIONS.md

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+# CLAUDE.md - Guidelines for Agentic Coding
+
+## Build/Run/Test Commands
+- **Build WASM binary**: `task build` or `make build`
+- **Generate code**: `task gen` or `make generate`
+- **Run tests**: `task test`
+- **Run single test**: `go test -v ./path/to/package -run TestName`
+- **Development workflow**: `task` (runs test, generate, build sequence)
+
+## Code Style Guidelines
+- **Formatting**: Standard Go formatting with `gofmt`
+- **Imports**: Group standard library, third-party, and project imports
+- **Types**: Use descriptive type names; alias complex types (e.g., `type Vault = *echo.Echo`)
+- **Error Handling**: Always check errors; wrap with context when propagating
+- **Naming**:
+  - Packages: lowercase, concise nouns (e.g., `handlers`, `models`)
+  - Interfaces: action+er (e.g., `Querier`)
+  - Variables: camelCase for local, PascalCase for exported
+- **Structure**: Follow Go's standard project layout
+- **Comments**: Add godoc comments for all exported functions/types
+- **WASM Context**: Use internal/context package for WASM-specific context