docs: add quick start guide (PR #9245)

Add docs/quickstart.md with end-to-end quick start guide covering
prerequisites, installation, project creation, resource registration,
plan/apply workflow, and troubleshooting.

Update mkdocs.yml navigation to include Quick Start page and rename
ADR-028 title to Skill/Tool Abstraction Definition.

Update CHANGELOG.md with quick start guide entry.

Closes #9245

docs/quickstart.md

@@ -0,0 +1,43 @@
+# Quick Start Guide
+
+This quick start guide will walk you through creating a new project, registering a resource, running a plan, and applying changes with CleverAgents.
+
+## Prerequisites
+
+- Python 3.11+ and virtualenv
+- Git
+- A working CleverAgents installation (see development/testing.md for details)
+
+## Install (local development)
+
+```bash
+python -m venv .venv
+source .venv/bin/activate
+pip install -e .[dev]
+```
+
+## Create a new project
+
+```bash
+# Create a new directory for your project
+mkdir my-project && cd my-project
+# Initialize a CleverAgents project (example command)
+cleveragents init --name my-project
+```
+
+## Register a resource
+
+Create a resource file under `resources/` (example YAML) and register it with the CLI or API.
+
+## Plan and apply
+
+```bash
+# Generate a plan
+cleveragents plan --project my-project
+# Review the plan, then apply
+cleveragents apply --project my-project
+```
+
+## Troubleshooting
+
+If you encounter issues running the examples above, consult `docs/development/testing.md` and the project README for local development tips.