build: add preflight validator family for versions/manifest/changelog drift

Establishes the local pre-push gate. preflight.sh runs four blocks: version
consistency, manifest shape (Icon plus all ImageUrls), changelog sync, plus a
release build as compile-health smoke. setup-hooks.sh wires core.hooksPath to
.githooks. .gitignore opens scripts/ for tracking (setup-dev-env.sh stays
private). Test execution itself lives in a separate local repository and is
not part of this codebase.

scripts/preflight.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# preflight.sh — pre-push gate. Blocks A/B/C verify config drift; Block D is a
+# headless `dotnet build` to catch compile-time API drift. Test execution lives
+# in the local Build-Suite repo and is NOT part of this preflight.
+
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT"
+
+echo "==> preflight: Block A — version consistency"
+./scripts/verify-version-consistency.sh
+
+echo "==> preflight: Block B — manifest shape"
+./scripts/verify-manifest-shape.sh
+
+echo "==> preflight: Block C — changelog sync"
+./scripts/verify-changelog-sync.sh
+
+echo "==> preflight: Block D — plugin compile health"
+dotnet build HellionChat/HellionChat.csproj --configuration Release --nologo --verbosity quiet
+
+echo "==> preflight: ALL GREEN"