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/architecture.md

@@ -0,0 +1,22 @@
+# Architecture
+
+## Code Layout
+
+```
+main.go              — entrypoint, calls cmd.Execute()
+cmd/                  — cobra commands (root + subcommands)
+internal/             — private application packages
+docs/                 — project documentation
+```
+
+## Packages
+
+| Package | Purpose | Status |
+|---------|---------|--------|
+| `cmd` | CLI command definitions | ✅ skeleton |
+| `internal/config` | Configuration loading and parsing | ⬜ planned |
+| `internal/controllers` | HTTP request handlers | ⬜ planned |
+| `internal/auth` | Authentication (JWT) | ⬜ planned |
+| `internal/storage` | File storage abstraction | ⬜ planned |
+
+Add new rows as packages are created.