Initialize project skeleton with CLI and documentation

Add initial project structure including:
- Go module with Cobra CLI dependency
- Root command and main entrypoint
- Basic documentation (README, AGENTS.md, architecture, decisions,
  development, roadmap)
- Configuration example and gitignore
- Tool version management with mise
- Comprehensive project rules and conventions

docs/roadmap.md

@@ -0,0 +1,24 @@
+# Roadmap
+
+See `README.md` for high-level feature list. This file tracks detailed progress.
+
+## v0
+
+| Feature | Status | Notes |
+|---------|--------|-------|
+| CLI config management | ⬜ planned | |
+| JWT authentication | ⬜ planned | |
+| File upload/download/manage APIs | ⬜ planned | |
+| Admin endpoints | ⬜ planned | |
+| WebDAV | ⬜ planned | |
+
+## Future
+
+| Feature | Status | Notes |
+|---------|--------|-------|
+| Image server | ⬜ planned | |
+| Pastebin & code snippets | ⬜ planned | |
+| S3 storage backend | ⬜ planned | |
+| Nextcloud-compatible API | ⬜ planned | |
+
+Update status after completing related work.