Run full bootstrap in integration tests; fix pnpm setup shell detection

- Integration tests now run the full bootstrap (system + flatpak + custom +
  AI + VM packages) instead of '--only custom --no-vm --no-ai', so that
  custom-package prerequisites (zsh, gh, etc.) installed via SystemPackages
  are actually available.
- Fix 'pnpm setup' failing with ERR_PNPM_UNKNOWN_SHELL in CI containers
  by exporting SHELL=/bin/bash before invoking it.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

post.go

@@ -250,7 +250,7 @@ func ensureNodeLTS() {
 		return
 	}
 	fmt.Println("[pnpm] Running pnpm setup to configure PATH ...")
-	if !runShell(`bash -c 'source ~/.nvm/nvm.sh && pnpm setup'`, CmdOpts{}).OK() {
+	if !runShell(`bash -c 'export SHELL=/bin/bash && source ~/.nvm/nvm.sh && pnpm setup'`, CmdOpts{}).OK() {
 		errLog("pnpm setup failed")
 	}
 }