feat(server,app,website): prefix service URLs with project slug

Service hostnames now follow DNS convention with a project label so
independently opened projects no longer collide on routes like
`web.localhost`. Format becomes `{script}.{project}.localhost` for
default branches and `{script}.{branch}.{project}.localhost` for other
branches. The project slug comes from the GitHub repository name when a
remote exists, otherwise from the workspace directory basename.

Server changes:
- `buildScriptHostname` takes `{ projectSlug, branchName, scriptName }`
  and slugifies all labels at the boundary; `untitled` fallback only
  applies at hostname-label sites, never to shared `slugify`.
- `deriveProjectSlug(cwd)` and `parseGitHubRepoNameFromRemote` derive
  the slug; GitHub URL parsing now requires `host === "github.com"` to
  avoid embedded-path false matches.
- `ScriptRouteEntry` carries `projectSlug`; branch-rename handler reuses
  it instead of re-reading git in hot paths.
- Status projection derives slug once per call and uses route hostname
  when available; only falls back to building when no route exists.
- Spawn cleanup removes routes by `{ workspaceId, scriptName }` so
  cleanup after a branch rename doesn't leave a stale entry behind.

App and shared message tests updated to the new fixture shape; service
URLs continue to be opaque server-provided strings.

Landing-page service URL examples updated; allowlist docs unchanged.

packages/server/src/utils/script-hostname.ts

@@ -1,12 +1,27 @@
 import { slugify } from "./worktree.js";
 
-export function buildScriptHostname(branchName: string | null, scriptName: string): string {
-  const serviceHostnameLabel = slugify(scriptName);
+type BuildScriptHostnameOptions = {
+  projectSlug: string;
+  branchName: string | null;
+  scriptName: string;
+};
+
+function toHostnameLabel(value: string): string {
+  return slugify(value) || "untitled";
+}
+
+export function buildScriptHostname({
+  projectSlug,
+  branchName,
+  scriptName,
+}: BuildScriptHostnameOptions): string {
+  const serviceHostnameLabel = toHostnameLabel(scriptName);
+  const projectHostnameLabel = toHostnameLabel(projectSlug);
   const isDefaultBranch = branchName === null || branchName === "main" || branchName === "master";
 
   if (isDefaultBranch) {
-    return `${serviceHostnameLabel}.localhost`;
+    return `${serviceHostnameLabel}.${projectHostnameLabel}.localhost`;
   }
 
-  return `${slugify(branchName)}.${serviceHostnameLabel}.localhost`;
+  return `${serviceHostnameLabel}.${toHostnameLabel(branchName)}.${projectHostnameLabel}.localhost`;
 }