setup wizard: fix routing, DHCP, WiFi AP, firewall, and deploy task

Setup script fixes:
- _cidr_to_mask: pad to 4 octets (/24 -> 255.255.255.0)
- UCI quoting: remove embedded shell quotes from uci set calls
- Bridge ports: auto-detect zt* interface instead of hardcoding ztabc0
- Bridge netmask: default to /23 (255.255.254.0) for ZT+WIBLAN
- DHCP/WiFi AP: reference interface name (zt_wiblan) not device name (br_zt)
- Firewall zone: add zt_wiblan to LAN zone for nftables fw4
- ZT IP persistence: ensure ZT-assigned IP stays on interface for ARP
- Exit gateway routing: table 100/101 route via exit gateway, not self
- New setup-wifi-ap subcommand for WIBLAN WiFi AP

UBUS handler:
- Add setup-wifi-ap to validation regex and error message

Deploy task:
- Auto-discover files from root/ and htdocs/ instead of hardcoded list
- Clear LuCI cache before restarting services

Documentation:
- New docs/SETUP-GATEWAY.md with architecture, config, pitfalls, checklist
- Updated docs/INSTALL.md with deploy task and setup wizard sections
- Updated docs/PROGRESS.md with session log and learnings

root/usr/share/rpcd/ucode/zt-gateway.uc

@@ -301,10 +301,10 @@ return {
 			},
 			call: function(req) {
 				const command = req.args?.command;
-				if (!command || !match(command, /^(status|setup-bridge|setup-routing|setup-dhcp|setup-hotplug|setup-persistence|setup-all)$/)) {
+				if (!command || !match(command, /^(status|setup-bridge|setup-routing|setup-dhcp|setup-wifi-ap|setup-hotplug|setup-persistence|setup-all)$/)) {
 					return {
 						success: false,
-						message: 'Invalid command. Valid: status, setup-bridge, setup-routing, setup-dhcp, setup-hotplug, setup-persistence, setup-all'
+						message: 'Invalid command. Valid: status, setup-bridge, setup-routing, setup-dhcp, setup-wifi-ap, setup-hotplug, setup-persistence, setup-all'
 					};
 				}