Add a firewall page to the web UI

Allow rules between zones (LANs and tunnels) are edited on their own page:
from, to, protocol, ports, destination. Port forwards and rules with more
options are listed and kept as they are.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AeFqV9dZrK6nipHkPfyM4F

pkgs/router-webui/templates/firewall.html

@@ -0,0 +1,45 @@
+{{define "content"}}
+{{with .Data}}
+{{$e := .Errors}}
+<p class="hint">Traffic between zones is denied unless a rule allows it. A rule works in one direction only
+   (replies are always allowed), so letting two networks talk to each other takes two rules.
+   Traffic inside a zone is always allowed. A zone is a LAN or a WireGuard tunnel (named on the WireGuard page).</p>
+<form method="post" action="/firewall">
+  <input type="hidden" name="csrf" value="{{$.CSRF}}">
+  <fieldset>
+    <legend>Allow rules</legend>
+    <input type="hidden" name="rows" value="{{len .Rows}}">
+    <table>
+      <tr><th>From</th><th>To</th><th>Protocol</th><th>Ports</th><th>Only to address</th><th>Remove</th></tr>
+      {{range $i, $r := .Rows}}
+      <tr>
+        <td><select name="rule.{{$i}}.from"><option value=""></option>
+          {{range $.Data.Zones}}<option value="{{.}}" {{if eq . $r.From}}selected{{end}}>{{.}}</option>{{end}}
+        </select></td>
+        <td><select name="rule.{{$i}}.to"><option value=""></option>
+          {{range $.Data.Zones}}<option value="{{.}}" {{if eq . $r.To}}selected{{end}}>{{.}}</option>{{end}}
+        </select></td>
+        <td><select name="rule.{{$i}}.protocol">
+          {{range $p := list "any" "tcp" "udp" "icmp"}}<option value="{{$p}}" {{if eq $p $r.Protocol}}selected{{end}}>{{$p}}</option>{{end}}
+        </select></td>
+        <td><input name="rule.{{$i}}.ports" value="{{$r.Ports}}" size="14" placeholder="all"></td>
+        <td><input name="rule.{{$i}}.destination" value="{{$r.Destination}}" size="16" spellcheck="false" placeholder="whole zone"></td>
+        <td>{{if or $r.From $r.To}}<input type="checkbox" name="rule.{{$i}}.remove">{{end}}</td>
+      </tr>
+      {{range $f := list "from" "to" "protocol" "ports" "destination"}}{{with index $e (printf "rule[%d].%s" $i $f)}}<tr><td colspan="6" class="field-error">{{$f}}: {{.}}</td></tr>{{end}}{{end}}
+      {{end}}
+    </table>
+    <p class="hint">Fill in the last row to add a rule. Ports apply to tcp and udp: <code>22, 443, 5000-5100</code>.</p>
+  </fieldset>
+  <button>Save</button>
+</form>
+
+{{if .Other}}
+<section>
+  <h2>Other rules</h2>
+  <p class="muted">Port forwards and rules with more options are kept as they are; change them in <code>settings.json</code>.</p>
+  <ul>{{range .Other}}<li>{{.}}</li>{{end}}</ul>
+</section>
+{{end}}
+{{end}}
+{{end}}