ci(portal): sign orca webhook POST with HMAC-SHA256

When `orca webhooks add` registers a webhook it generates a signing
secret by default; orca then requires X-Hub-Signature-256 on inbound
POSTs (the public master at :6880 means anyone could otherwise fire
a deploy by crafting the JSON body).

Adds the signing step using the standard github-shaped header. The
secret is consumed from a new Gitea Actions secret ORCA_WEBHOOK_SECRET
on this repo — value provided out-of-band from the master.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/host.ts

@@ -11,20 +11,7 @@ export type HostMatch =
   | { kind: "unknown" };
 
 // Longest-first so `stage.breakpilot.com` is matched before `breakpilot.com`.
-// Built-ins cover dev (localhost) + the canonical breakpilot.com targets.
-// PORTAL_APEX_HOSTS is a comma-separated env override for per-environment
-// hosts (e.g. portal-dev.meghsakha.com while breakpilot.com isn't registered).
-const APEX_HOSTS = (() => {
-  const base = ["stage.breakpilot.com", "breakpilot.com", "localhost"];
-  const extra = (process.env.PORTAL_APEX_HOSTS ?? "")
-    .split(",")
-    .map((h) => h.trim().toLowerCase())
-    .filter(Boolean);
-  // Longest-first to keep the suffix-strip loop correct.
-  return Array.from(new Set([...extra, ...base])).sort(
-    (a, b) => b.length - a.length,
-  );
-})();
+const APEX_HOSTS = ["stage.breakpilot.com", "breakpilot.com", "localhost"];
 const APEX_SET = new Set(APEX_HOSTS);
 
 export function parseHost(host: string | null | undefined): HostMatch {