Harden repository for agent-guided contribution workflow

[senolcolak]

Context

The repository structure and AGENTS.md are now in place. The next step is to make RustChat consistently usable by human contributors and AI coding agents such as Codex, Claude Code, or similar tools.

This should not add unnecessary ceremony. The goal is a lean, practical contribution workflow inspired by mature Rust projects such as Turso: clear repo map, clear testing expectations, predictable CI, and explicit agent guardrails.

Scope

• Review AGENTS.md against the current repository layout and make sure all paths, crate names, and commands are accurate.
• Ensure README.md and CONTRIBUTING.md point contributors to AGENTS.md where appropriate.
• Add or update lightweight agent/contributor docs, for example:
  • docs/agent-guides/testing.md
  • docs/agent-guides/code-quality.md
  • docs/agent-guides/pr-workflow.md
  • docs/architecture/overview.md
• Document the expected local validation commands:
  • cargo fmt --check
  • cargo clippy --workspace --all-features --all-targets -- --deny warnings
  • cargo test --workspace
• Review CI and make sure the same basic quality gates are enforced.
• Add or update PR / issue templates if missing.

RustChat-specific notes

Please make the contribution guidance explicit about the main RustChat boundaries:

• realtime/chat server behavior
• API and protocol changes
• auth/session handling
• persistence/storage behavior
• frontend/client-facing behavior, if applicable

Protocol or storage changes should include migration notes or compatibility notes where relevant.

Acceptance criteria

• AGENTS.md accurately reflects the current RustChat repo layout.
• The main build, lint, format, and test commands are documented and work locally.
• CI enforces the same baseline quality gates.
• README.md / CONTRIBUTING.md link to the agent/contributor workflow.
• At least one short agent guide exists for testing and PR workflow.
• The repo makes it clear what an AI agent may change and what requires human review.
• The guidance stays lean and does not introduce unnecessary process overhead.

[senolcolak]

AGENTS.md needs to be %100 specific to the project, combine the AGENTS.md with the SPECS so that the development would never miss the principles and standards