Add example config and test harness

[sbugalski]

Description

New users have to read through the wiki to understand Dippy's config syntax and figure out a working setup from scratch. An annotated example config and a test script would lower the barrier to entry.

Proposal

Add two files under examples/:

examples/config — Annotated starter config covering:

• Python, uv, Git, Docker, npm, PowerShell, curl/wget
• MCP tool rules (read-only allow, mutating ask, destructive deny)
• Shell redirect protection (~, .env, system paths)
• Home directory and system path protection
• Prominent warnings about the last-match-wins ordering footgun

examples/test-config.sh — Test harness (45 tests across 6 categories):

1. MCP tools (read-only, destructive, mutating, catch-all)
2. Shell redirects (~, .env, /tmp, ~/.ssh, ~/.aws)
3. System paths (/etc, /usr, ~/.ssh)
4. Home directory protection (rm, mv, cp, exceptions)
5. Commands (git, python, uv, npm, docker, rm -rf, pwsh)
6. Pipelines / compound commands (&&)

Auto-detects dippy/dippy.exe, CI-friendly (exit $FAIL).

Usage

cp examples/config ~/.dippy/config   # customize to your needs
bash examples/test-config.sh         # validate decisions