docs: add comprehensive project documentation and reduce redundancy

Add CODE_GUIDELINES.md, database schema docs, and development-progress-log.md.
Refactor README.md to eliminate redundant information by linking to detailed docs.
Establish clear documentation hierarchy for better maintainability.

README.md

@@ -161,27 +161,33 @@ Now you can log in to Mila via OIDC!
 
 ## 🏗️ Architecture
 
-- **Backend:** Elixir, Phoenix, LiveView, Ash Framework  
-- **Frontend:** Phoenix LiveView + DaisyUI + Heroicons  
-- **Database:** PostgreSQL (via AshPostgres)  
-- **Auth:** AshAuthentication (OIDC + password strategy)  
-- **Mail:** Swoosh  
-- **i18n:** Gettext  
+**Tech Stack Overview:**
+- **Backend:** Elixir + Phoenix + Ash Framework  
+- **Frontend:** Phoenix LiveView + Tailwind CSS + DaisyUI  
+- **Database:** PostgreSQL  
+- **Auth:** AshAuthentication (OIDC + password)
 
-Code structure:  
-- `lib/mv/` — core Ash resources/domains (`Accounts`, `Membership`)  
+**Code Structure:**
+- `lib/accounts/` & `lib/membership/` — Ash resources and domains
 - `lib/mv_web/` — Phoenix controllers, LiveViews, components  
-- `assets/` — frontend assets (Tailwind, JS, etc.)  
+- `assets/` — Tailwind, JavaScript, static files
+
+📚 **Full tech stack details:** See [`CODE_GUIDELINES.md`](CODE_GUIDELINES.md)  
+📖 **Implementation history:** See [`docs/development-progress-log.md`](docs/development-progress-log.md)  
+🗄️ **Database schema:** See [`docs/database-schema-readme.md`](docs/database-schema-readme.md)  
 
 ## 🧑‍💻 Development
 
-Useful `just` commands:  
-- `just run` — start DB, Mailcrab, Rauthy, app  
-- `just test` — run tests  
-- `just lint` — run code style checks (credo, formatter)  
-- `just audit` — run security audits  
-- `just reset-database` — reset local DB  
-- `just regen-migrations <name>` — regenerate migrations  
+**Common commands:**
+```bash
+just run                      # Start full dev environment
+just test                     # Run test suite
+just lint                     # Code style checks
+just audit                    # Security audits
+just reset-database           # Reset local DB
+```
+
+📚 **Full development guidelines:** See [`CODE_GUIDELINES.md`](CODE_GUIDELINES.md)  
 
 ## 📦 Production Deployment