platform: BreadClient command/health, fail-closed get.sh, registry README

Add BreadClient::command (unsourced bread.command.<app>.<verb> emit) plus
health/api_version, and a clap-free screenshot_cli helper for the next pin.
get.sh now dies if minisign or .minisig is missing — checksum-only is not
enough to install. Generate the README products table from the registry,
and refresh release-channels/CONTRIBUTING/CLAUDE.md to match.

scripts/gen-readme-products.sh

@@ -0,0 +1,77 @@
+#!/usr/bin/env bash
+# Rewrite the marked Products table in README.md from
+# registry/bread-ecosystem.toml (the source of truth).
+#
+# Markers (must exist in README.md):
+#   <!-- gen-readme-products:start -->
+#   ...generated markdown...
+#   <!-- gen-readme-products:end -->
+#
+# Optional per-product `notes` in the registry is appended to the
+# description after an em-dash (used for "homelab, not BOS" / "not in ISO").
+#
+# Usage: scripts/gen-readme-products.sh
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+REGISTRY="${SCRIPT_DIR}/registry/bread-ecosystem.toml"
+README="${SCRIPT_DIR}/README.md"
+START="<!-- gen-readme-products:start -->"
+END="<!-- gen-readme-products:end -->"
+
+if [[ ! -f "${REGISTRY}" ]]; then
+    echo "error: registry not found at ${REGISTRY}" >&2
+    exit 2
+fi
+if [[ ! -f "${README}" ]]; then
+    echo "error: README not found at ${README}" >&2
+    exit 2
+fi
+
+python3 - "${REGISTRY}" "${README}" "${START}" "${END}" <<'PY'
+import sys
+from pathlib import Path
+
+try:
+    import tomllib
+except ImportError:  # pragma: no cover — 3.11+ is required
+    import tomli as tomllib  # type: ignore
+
+registry_path, readme_path, start, end = sys.argv[1:]
+
+with open(registry_path, "rb") as f:
+    registry = tomllib.load(f)
+
+products = registry.get("products") or []
+if not products:
+    print("error: registry has no [[products]]", file=sys.stderr)
+    sys.exit(1)
+
+lines = ["| Package | Description |", "|---------|-------------|"]
+for product in products:
+    name = product["name"]
+    desc = str(product.get("description") or "").replace("|", "\\|")
+    notes = str(product.get("notes") or "").replace("|", "\\|")
+    if notes:
+        desc = f"{desc} — {notes}"
+    lines.append(f"| `{name}` | {desc} |")
+table = "\n".join(lines)
+
+readme = Path(readme_path)
+text = readme.read_text()
+start_at = text.find(start)
+end_at = text.find(end)
+if start_at < 0 or end_at < 0 or end_at < start_at:
+    print(
+        f"error: README.md is missing markers {start!r} / {end!r}",
+        file=sys.stderr,
+    )
+    sys.exit(1)
+
+rewritten = text[:start_at] + start + "\n\n" + table + "\n\n" + end + text[end_at + len(end):]
+if rewritten != text:
+    readme.write_text(rewritten)
+    print(f"updated {readme_path} ({len(products)} products)")
+else:
+    print(f"{readme_path} already matches the registry ({len(products)} products)")
+PY