feat(site): добавлен MkDocs Material сайт с CI/CD на GitHub Pages

- Зачем:
  - роадмап нуждается в презентабельном виде с навигацией и поиском, а не только GitHub README.
- Что:
  - создан mkdocs.yml (Material, docs_dir: ., поиск на русском, тёмная/светлая тема).
  - создан .github/workflows/deploy-site.yml (push в main → сборка → GitHub Pages).
  - адаптирован Markdown для dual compatibility (GitHub + MkDocs): пустые строки перед списками, отступы 2sp→4sp, заголовки README #→## для корректного TOC.
  - заменены em-dash на запятые в 4 заголовках dwh-modeling/README.md (фикс расхождения якорей).
  - добавлены правила Markdown Style и команды MkDocs/Playwright в AGENTS.md.
- Проверка:
  - uv run --with 'mkdocs-material==9.6.14' --with 'mkdocs-same-dir==0.1.3' mkdocs build --strict

AGENTS.md

@@ -1,9 +1,12 @@
 # Repository Guidelines
 
 ## Project Structure & Module Organization
-- Root `README.md` describes the learning roadmap (RU).
+- Root `README.md` describes the learning roadmap (RU) and serves as the main page of the MkDocs site.
 - `dwh-modeling/` contains the article and demo DWH model; SQL lives in `dwh-modeling/sql` as ordered scripts `01_...sql`–`09_...sql` (07–09 are homework DDL, template and solution).
 - `postgres-bookings/` is a Dockerized PostgreSQL + demo “bookings” DB; start it first, then apply DWH scripts against the `demo` database.
+- `mkdocs.yml` — MkDocs Material config; `docs_dir: .` (repo root = site root). Excluded dirs: `project/`, `postgres-bookings/`, `.github/`, `.claude/`.
+- `.github/workflows/deploy-site.yml` — CI/CD: push to `main` → build → deploy to GitHub Pages.
+- `project/` — PRD and ADR (excluded from site).
 
 ## Build, Test, and Development Commands
 - Start demo Postgres:  
@@ -20,6 +23,45 @@
 - SQL files: keep numeric prefixes (`01_`, `02_`, …) to reflect execution order and use descriptive suffixes like `ddl_*` / `dml_*`.
 - Shell: target `bash`, prefer simple, POSIX-friendly constructs; mirror the style of existing scripts in `postgres-bookings/`.
 
+## Markdown Style (dual-compatible: GitHub + MkDocs Material)
+
+All `.md` files MUST render correctly on both GitHub and the MkDocs Material site. Follow these rules:
+
+**Headings:**
+- `README.md` (root): start from `##` (H2). Do NOT use `#` (H1) — MkDocs uses H1 as page title, multiple H1s break the right-sidebar TOC.
+- `dwh-modeling/*.md`: may use `#` (H1) since each file is a separate page on the site.
+
+**Lists:**
+- Always leave a **blank line before the first list item** after a paragraph, heading, or any non-list text. Python-Markdown (MkDocs) requires this; GitHub tolerates its absence but blank lines don't hurt.
+- Use **4-space indentation** for nested lists (not 2-space). GitHub supports both, Python-Markdown requires 4.
+- Example:
+  ```markdown
+  Some introductory text:
+
+  - Item one
+  - Item two
+      - Nested item (4 spaces)
+  ```
+
+**Links:**
+- Internal links: always use **relative paths to `.md` files**: `[text](dwh-modeling/SCD.md)`. MkDocs resolves them automatically.
+- Anchor links: use lowercase slugs with single hyphens. Avoid em-dash `—` in headings (it produces `--` in MkDocs slugs vs `-` on GitHub). Use commas or colons instead.
+
+**Special characters in headings:**
+- OK: colons `:`, commas `,`, parentheses `()`, guillemets `«»` — stripped equally by both platforms.
+- Avoid: em-dash `—`, en-dash `–` — slug behavior differs between GitHub and MkDocs.
+
+## MkDocs Site Commands
+- Local preview (user starts, ask user to run via `!`):
+  `uv run --with 'mkdocs-material==9.6.14' --with 'mkdocs-same-dir==0.1.3' mkdocs serve`
+- Build with strict validation (catches broken links/anchors):
+  `uv run --with 'mkdocs-material==9.6.14' --with 'mkdocs-same-dir==0.1.3' mkdocs build --strict`
+- Visual check via Playwright (when `mkdocs serve` is running on port 8000):
+  `npx playwright screenshot --viewport-size='1280,800' 'http://127.0.0.1:8000/#anchor' /path/to/screenshot.png`
+  Then read the screenshot with the Read tool to inspect rendering. Use `--viewport-size='1280,2000'` for tall pages.
+- Kill stuck dev server: `lsof -ti :8000 | xargs kill`
+- Site URL: `https://dementev-dev.github.io/de-roadmap/`
+
 ## Testing Guidelines
 - There is no dedicated test framework; treat SQL scripts as executable documentation.
 - For `dwh-modeling/sql`, run scripts sequentially and rerun `04_validation.sql` after changes to ensure the demo model still loads and basic checks pass.