Add multi-distro support for deckies

Introduces DistroProfile catalog (9 distros: Debian, Ubuntu 20/22,
Rocky 9, CentOS 7, Alpine, Fedora, Kali, Arch) with distro-styled
hostname generation. Adds --distro and --randomize-distros CLI flags,
a `decnet distros` listing command, and fixes composer.py which was
ignoring per-decky base_image in favour of a hardcoded Debian constant.

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

decnet/distros.py

@@ -0,0 +1,119 @@
+"""
+Distro profiles for DECNET deckies.
+
+Each profile maps a human-readable slug to a Docker image and OS metadata used
+to make deckies look like heterogeneous real machines on the LAN.
+"""
+
+import random
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class DistroProfile:
+    slug: str           # CLI-facing identifier, e.g. "debian", "rocky9"
+    image: str          # Docker image tag
+    display_name: str   # Human-readable label shown in tables
+    hostname_style: str # "generic" | "rhel" | "minimal" | "rolling"
+
+
+DISTROS: dict[str, DistroProfile] = {
+    "debian": DistroProfile(
+        slug="debian",
+        image="debian:bookworm-slim",
+        display_name="Debian 12 (Bookworm)",
+        hostname_style="generic",
+    ),
+    "ubuntu22": DistroProfile(
+        slug="ubuntu22",
+        image="ubuntu:22.04",
+        display_name="Ubuntu 22.04 LTS (Jammy)",
+        hostname_style="generic",
+    ),
+    "ubuntu20": DistroProfile(
+        slug="ubuntu20",
+        image="ubuntu:20.04",
+        display_name="Ubuntu 20.04 LTS (Focal)",
+        hostname_style="generic",
+    ),
+    "rocky9": DistroProfile(
+        slug="rocky9",
+        image="rockylinux:9-minimal",
+        display_name="Rocky Linux 9",
+        hostname_style="rhel",
+    ),
+    "centos7": DistroProfile(
+        slug="centos7",
+        image="centos:7",
+        display_name="CentOS 7",
+        hostname_style="rhel",
+    ),
+    "alpine": DistroProfile(
+        slug="alpine",
+        image="alpine:3.19",
+        display_name="Alpine Linux 3.19",
+        hostname_style="minimal",
+    ),
+    "fedora": DistroProfile(
+        slug="fedora",
+        image="fedora:39",
+        display_name="Fedora 39",
+        hostname_style="rhel",
+    ),
+    "kali": DistroProfile(
+        slug="kali",
+        image="kalilinux/kali-rolling",
+        display_name="Kali Linux (Rolling)",
+        hostname_style="rolling",
+    ),
+    "arch": DistroProfile(
+        slug="arch",
+        image="archlinux:latest",
+        display_name="Arch Linux",
+        hostname_style="rolling",
+    ),
+}
+
+_NAME_WORDS = [
+    "alpha", "bravo", "charlie", "delta", "echo",
+    "foxtrot", "golf", "hotel", "india", "juliet",
+    "kilo", "lima", "mike", "nova", "oscar",
+    "prod", "web", "db", "mail", "proxy",
+    "dev", "stage", "backup", "monitor", "files",
+]
+
+
+def random_hostname(distro_slug: str = "debian") -> str:
+    """Generate a plausible hostname for the given distro style."""
+    profile = DISTROS.get(distro_slug)
+    style = profile.hostname_style if profile else "generic"
+    word = random.choice(_NAME_WORDS)
+    num = random.randint(10, 99)
+
+    if style == "rhel":
+        # RHEL/CentOS/Fedora convention: word+num.localdomain
+        return f"{word}{num}.localdomain"
+    elif style == "minimal":
+        return f"{word}-{num}"
+    elif style == "rolling":
+        # Kali/Arch: just a word, no suffix
+        return f"{word}-{random.choice(_NAME_WORDS)}"
+    else:
+        # Debian/Ubuntu: SRV-WORD-nn
+        return f"SRV-{word.upper()}-{num}"
+
+
+def get_distro(slug: str) -> DistroProfile:
+    if slug not in DISTROS:
+        raise ValueError(
+            f"Unknown distro '{slug}'. Available: {', '.join(sorted(DISTROS))}"
+        )
+    return DISTROS[slug]
+
+
+def random_distro() -> DistroProfile:
+    return random.choice(list(DISTROS.values()))
+
+
+def all_distros() -> dict[str, DistroProfile]:
+    return dict(DISTROS)