feat: add wave 1 plugins (dns, encode, hash, defang, revshell, cidr)

All pure stdlib, zero external dependencies:
- dns: raw UDP resolver with A/AAAA/MX/NS/TXT/CNAME/PTR/SOA
- encode: base64, hex, URL, ROT13 encode/decode
- hash: md5/sha1/sha256/sha512 generation + type identification
- defang: IOC defanging/refanging for safe sharing
- revshell: reverse shell one-liners for 11 languages
- cidr: subnet calculator with IP membership check

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

plugins/cidr.py

@@ -0,0 +1,78 @@
+"""Plugin: CIDR/subnet calculator."""
+
+from __future__ import annotations
+
+import ipaddress
+
+from derp.plugin import command
+
+
+@command("cidr", help="Subnet info: !cidr <network> | !cidr contains <net> <ip>")
+async def cmd_cidr(bot, message):
+    """Calculate subnet properties or check IP membership.
+
+    !cidr 192.168.1.0/24
+    !cidr contains 10.0.0.0/8 10.1.2.3
+    """
+    parts = message.text.split()
+    if len(parts) < 2:
+        await bot.reply(message, "Usage: !cidr <network> | !cidr contains <net> <ip>")
+        return
+
+    subcmd = parts[1].lower()
+
+    if subcmd == "contains" and len(parts) >= 4:
+        await _contains(bot, message, parts[2], parts[3])
+    elif subcmd == "contains":
+        await bot.reply(message, "Usage: !cidr contains <network> <ip>")
+    else:
+        await _info(bot, message, parts[1])
+
+
+async def _info(bot, message, network_str: str) -> None:
+    """Show subnet information."""
+    try:
+        net = ipaddress.ip_network(network_str, strict=False)
+    except ValueError:
+        await bot.reply(message, f"Invalid network: {network_str}")
+        return
+
+    if isinstance(net, ipaddress.IPv4Network):
+        host_count = net.num_addresses - 2 if net.prefixlen < 31 else net.num_addresses
+        parts = [
+            f"net:{net.network_address}/{net.prefixlen}",
+            f"range:{net[0]}-{net[-1]}",
+            f"hosts:{host_count}",
+            f"mask:{net.netmask}",
+            f"wildcard:{net.hostmask}",
+        ]
+        if net.prefixlen < 31:
+            parts.append(f"broadcast:{net.broadcast_address}")
+    else:
+        parts = [
+            f"net:{net.network_address}/{net.prefixlen}",
+            f"range:{net[0]}-{net[-1]}",
+            f"hosts:{net.num_addresses}",
+        ]
+
+    await bot.reply(message, " | ".join(parts))
+
+
+async def _contains(bot, message, network_str: str, ip_str: str) -> None:
+    """Check if an IP belongs to a network."""
+    try:
+        net = ipaddress.ip_network(network_str, strict=False)
+    except ValueError:
+        await bot.reply(message, f"Invalid network: {network_str}")
+        return
+
+    try:
+        addr = ipaddress.ip_address(ip_str)
+    except ValueError:
+        await bot.reply(message, f"Invalid IP: {ip_str}")
+        return
+
+    if addr in net:
+        await bot.reply(message, f"{addr} is in {net}")
+    else:
+        await bot.reply(message, f"{addr} is NOT in {net}")