fix: untrack runtime config files and add them to .gitignore

These files are machine-specific and generated at runtime — they should
never have been committed. Remove from index (files kept on disk) and
add explicit gitignore rules to prevent future re-adds.

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

config/dhcp/dnsmasq.conf

@@ -1,32 +0,0 @@
-# Personal Internet Cell - dnsmasq Configuration
-# Provides DHCP and local DNS resolution
-
-# Interface to listen on
-interface=eth0
-bind-interfaces
-
-# DHCP configuration
-dhcp-range=172.20.1.50,172.20.1.150,12h
-dhcp-option=3,172.20.0.1  # Gateway
-dhcp-option=6,172.20.0.2  # DNS server
-dhcp-option=42,172.20.0.4 # NTP server
-
-# DNS configuration
-port=53
-domain=local.cell
-expand-hosts
-local=/local.cell/
-
-# DNS forwarding
-server=8.8.8.8
-server=1.1.1.1
-
-# Cache size
-cache-size=1000
-
-# Logging
-log-queries
-log-dhcp
-
-# Static leases (optional)
-# dhcp-host=00:11:22:33:44:55,192.168.1.100,mydevice