feat: Add SOLID principles and TDD reference documentation

- Created solid.md to document the SOLID principles for clean code practices.
- Created tdd.md to outline Test Driven Development principles and practices.
- Added kana-rust-backend-best-practice.md as a reference guide for building a Rust backend using Axum and SeaORM.
- Established push-flow-convention.md to enforce pre-commit and pre-push hooks with versioning rules.
- Introduced AGENTS.md to provide guidance on best practices and available commands for Kilo.
- Configured kilo.json to include new skills and agents for enhanced functionality.
- Added lefthook.yml for managing git hooks to ensure code quality and adherence to conventions.

AGENTS.md

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+# AGENTS.md
+
+This file provides guidance to Kilo when working with code in the zesdex repository.
+
+## Best Practice Conventions
+
+Zesdex follows Kana Engineering Best Practices:
+
+1. **Clean Architecture** — Strict domain/application/infrastructure/presentation layering.
+   - Domain has ZERO framework dependencies.
+   - Application depends only on domain.
+   - Infrastructure implements domain traits.
+   - DTOs cross layer boundaries, NOT entities.
+
+2. **Clean Code** — Functions under ~40 lines, one level of abstraction per function, descriptive names, no flag arguments, no commented-out code.
+
+3. **Documentation** — Every pub fn, struct, enum, and trait needs a doc comment (///) explaining what, flow, why, and return value.
+
+4. **Commit Convention** — Conventional Commits in Bahasa Indonesia: `feat(scope):`, `fix(scope):`, `chore:`, `docs:`.
+
+5. **Error Handling** — `anyhow::Result` and `anyhow::bail!` throughout. Log with `tracing` (never stderr).
+
+6. **Testing** — `#[cfg(test)] mod tests` blocks inline in production files. Tests are F.I.R.S.T. (Fast, Independent, Repeatable, Self-validating, Timely).
+
+7. **No Compiler Bypasses** — Never use `#[allow(...)]`, `#[expect(...)]`, or `#[allow(dead_code)]`. Fix the underlying code.
+
+8. **Boy Scout Rule** — Leave every module cleaner than you found it.
+
+## Available Agents
+
+- `@rust-engineer` — Rust clean architecture specialist (subagent).
+- `@code-reviewer` — Code review specialist (subagent).
+
+## Available Commands
+
+- `/check` — Run cargo check, clippy, and tests.
+- `/audit` — Code quality audit against clean-architecture best practices.
+- `/doc` — Generate or update doc comments.