chore: add install scripts, doctor command, and AGENTS.md

- Add one-line installer (scripts/install.sh) with platform detection
- Add doctor command (scripts/commands/doctor.sh) for environment diagnostics
- Add shared libraries: dependencies, docker, platform, validation
- Update README with quick-start installer instructions
- Add AGENTS.md with codebase patterns for AI agent context

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

README.md

@@ -35,13 +35,65 @@ Mosaic Stack is a modern, PDA-friendly platform designed to help users manage th
 
 ## Quick Start
 
+### One-Line Install (Recommended)
+
+The fastest way to get Mosaic Stack running on macOS or Linux:
+
+```bash
+curl -fsSL https://get.mosaicstack.dev | bash
+```
+
+This installer:
+
+- ✅ Detects your platform (macOS, Debian/Ubuntu, Arch, Fedora)
+- ✅ Installs all required dependencies (Docker, Node.js, etc.)
+- ✅ Generates secure secrets automatically
+- ✅ Configures the environment for you
+- ✅ Starts all services with Docker Compose
+- ✅ Validates the installation with health checks
+
+**Installer Options:**
+
+```bash
+# Non-interactive Docker deployment
+curl -fsSL https://get.mosaicstack.dev | bash -s -- --non-interactive --mode docker
+
+# Preview installation without making changes
+curl -fsSL https://get.mosaicstack.dev | bash -s -- --dry-run
+
+# With SSO and local Ollama
+curl -fsSL https://get.mosaicstack.dev | bash -s -- \
+  --mode docker \
+  --enable-sso --bundled-authentik \
+  --ollama-mode local
+
+# Skip dependency installation (if already installed)
+curl -fsSL https://get.mosaicstack.dev | bash -s -- --skip-deps
+```
+
+**After Installation:**
+
+```bash
+# Check system health
+./scripts/commands/doctor.sh
+
+# View service logs
+docker compose logs -f
+
+# Stop services
+docker compose down
+```
+
 ### Prerequisites
 
-- Node.js 20+ and pnpm 9+
-- PostgreSQL 17+ (or use Docker)
-- Docker & Docker Compose (optional, for turnkey deployment)
+If you prefer manual installation, you'll need:
 
-### Installation
+- **Docker mode:** Docker 24+ and Docker Compose
+- **Native mode:** Node.js 22+, pnpm 10+, PostgreSQL 17+
+
+The installer handles these automatically.
+
+### Manual Installation
 
 ```bash
 # Clone the repository