Add CLAUDE.md with topic-specific context docs

Split project context into .claude/context/ (architecture, server,
styling, standards) instead of one large file, referenced from a
minimal root CLAUDE.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,24 @@
+# Noo — Nextcloud Client
+
+A Flutter (Material 3) client for Nextcloud: browse files, view photos, check
+activity, manage shares/trash. Auth uses Nextcloud's Login Flow v2 — the app
+never collects a password directly, only a server address.
+
+Detailed, topic-specific context lives in `.claude/context/`. Read the
+relevant file(s) before working in that area rather than loading all of them:
+
+- [`architecture.md`](.claude/context/architecture.md) — folder layout, state
+  management, navigation/screen flow
+- [`server.md`](.claude/context/server.md) — Nextcloud API/WebDAV
+  integration, login flow, session persistence
+- [`styling.md`](.claude/context/styling.md) — theming, Material 3
+  conventions, fonts, reusable chrome widgets
+- [`standards.md`](.claude/context/standards.md) — code style, comment
+  conventions, linting, testing
+
+## Common commands
+
+```bash
+flutter test      # run tests
+flutter analyze   # static analysis / lints
+```