docs: add Material for MkDocs documentation site (English + Japanese)

Add a documentation website under website/, built from README.md and
README-Japanese.md and laid out with top-tab topics and a left sidebar (same
style as the Hayabusa docs). Designed to be hosted free on GitHub Pages.

- Pages: Overview (About, Features, Screenshots), Getting Started, Commands
  (Command List, Command Usage), Resources (Companion Projects, Other
  Resources, Changelog, Contributing)
- Custom landing page, theme, click-to-zoom screenshots
- Changelog synced from CHANGELOG.md at build time
- 15-language switcher via mkdocs-static-i18n: English + Japanese full content;
  the other 13 localize the UI and fall back to English until translated
- .github/workflows/docs.yml builds (mkdocs --strict) + deploys to GitHub Pages

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

website/scripts/sync_changelog.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+"""Regenerate the docs Changelog pages from the repo's CHANGELOG files.
+
+The Resources > Changelog pages mirror the root CHANGELOG.md /
+CHANGELOG-Japanese.md. The docs deploy workflow runs this before `mkdocs build`;
+the committed pages are a snapshot for local previews.
+
+Run from anywhere:  python website/scripts/sync_changelog.py
+"""
+import os
+import re
+
+ROOT = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+DOCS = os.path.join(ROOT, "website", "docs", "resources")
+
+NOTE_EN = (
+    "!!! info\n"
+    "    This page mirrors the project "
+    "[`CHANGELOG.md`](https://github.com/Yamato-Security/WELA/blob/main/CHANGELOG.md). "
+    "See the [Releases page](https://github.com/Yamato-Security/WELA/releases) for downloads."
+)
+NOTE_JA = (
+    '!!! info "情報"\n'
+    "    このページはプロジェクトの "
+    "[`CHANGELOG.md`](https://github.com/Yamato-Security/WELA/blob/main/CHANGELOG-Japanese.md) "
+    "を反映したものです。ダウンロードは "
+    "[リリースページ](https://github.com/Yamato-Security/WELA/releases) をご覧ください。"
+)
+
+_LIST = re.compile(r'^([-*+]|\d{1,9}[.)])\s+\S')
+_FENCE = re.compile(r'^\s*(```|~~~)')
+_HEADING = re.compile(r'^#{1,6}\s')
+
+
+def fix_tight_lists(text):
+    out, in_fence = [], False
+    for ln in text.split("\n"):
+        if _FENCE.match(ln):
+            in_fence = not in_fence
+        if not in_fence and _LIST.match(ln) and out:
+            p = out[-1]
+            if (p.strip() and not _LIST.match(p) and not _HEADING.match(p)
+                    and not p.lstrip().startswith(">") and not p.lstrip().startswith("|")
+                    and not re.match(r'^\s', p)):
+                out.append("")
+        out.append(ln)
+    return "\n".join(out)
+
+
+def build(src, title, note, dest):
+    lines = open(src, encoding="utf-8").read().split("\n")
+    body = lines[1:]
+    while body and body[0].strip() == "":
+        body.pop(0)
+    content = f"# {title}\n\n{note}\n\n" + "\n".join(body)
+    content = fix_tight_lists(content).rstrip() + "\n"
+    with open(dest, "w", encoding="utf-8") as f:
+        f.write(content)
+    print("wrote", os.path.relpath(dest, ROOT))
+
+
+def main():
+    build(os.path.join(ROOT, "CHANGELOG.md"), "Changelog", NOTE_EN,
+          os.path.join(DOCS, "changelog.md"))
+    build(os.path.join(ROOT, "CHANGELOG-Japanese.md"), "変更履歴", NOTE_JA,
+          os.path.join(DOCS, "changelog.ja.md"))
+
+
+if __name__ == "__main__":
+    main()