docs: add external documentation site content

Add structured documentation covering quickstart, architecture, core
concepts, API reference, adapter guides, CLI commands, deployment
options, and operator/developer guides.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/deploy/overview.md

@@ -0,0 +1,57 @@
+---
+title: Deployment Overview
+summary: Deployment modes at a glance
+---
+
+# Deployment Overview
+
+Paperclip supports three deployment configurations, from zero-friction local to internet-facing production.
+
+## Deployment Modes
+
+| Mode | Auth | Best For |
+|------|------|----------|
+| `local_trusted` | No login required | Single-operator local machine |
+| `authenticated` + `private` | Login required | Private network (Tailscale, VPN, LAN) |
+| `authenticated` + `public` | Login required | Internet-facing cloud deployment |
+
+## Quick Comparison
+
+### Local Trusted (Default)
+
+- Loopback-only host binding (localhost)
+- No human login flow
+- Fastest local startup
+- Best for: solo development and experimentation
+
+### Authenticated + Private
+
+- Login required via Better Auth
+- Binds to all interfaces for network access
+- Auto base URL mode (lower friction)
+- Best for: team access over Tailscale or local network
+
+### Authenticated + Public
+
+- Login required
+- Explicit public URL required
+- Stricter security checks
+- Best for: cloud hosting, internet-facing deployment
+
+## Choosing a Mode
+
+- **Just trying Paperclip?** Use `local_trusted` (the default)
+- **Sharing with a team on private network?** Use `authenticated` + `private`
+- **Deploying to the cloud?** Use `authenticated` + `public`
+
+Set the mode during onboarding:
+
+```sh
+pnpm paperclip onboard
+```
+
+Or update it later:
+
+```sh
+pnpm paperclip configure --section server
+```