fix: address multiple bugs from code review

- teardown_all.sh: replace `yes |` pipeline with `< <(yes)` process
  substitution to avoid SIGPIPE (exit 141) false failures under pipefail
- phase6_teardown.sh: extract push mirror `.id` instead of `.remote_name`
  to match the DELETE /push_mirrors/{id} API contract
- phase5_migrate_pipelines.sh: expand sed regex from `[a-z_]*` to
  `[a-z_.]*` to handle nested GitHub contexts like
  `github.event.pull_request.number`
- lib/common.sh: render_template now requires explicit variable list to
  prevent envsubst from eating Nginx variables ($host, $proxy_add_...)
- backup scripts: remove MacBook relay, use direct Unraid↔Fedora SCP;
  fix dump path to write to /data/ (mounted volume) instead of /tmp/
  (container-only); add unzip -t integrity verification
- preflight.sh: add --skip-port-checks flag for resuming with
  --start-from (ports already bound by earlier phases)
- run_all.sh: update run_step to pass extra args; use --skip-port-checks
  when --start-from > 1
- post-checks (phase4/7/9): wrap API calls in helper functions with
  >/dev/null redirection instead of passing -o /dev/null as API data
- phase8: replace GitHub archiving with [MIRROR] description marking
  and disable wiki/projects/Pages (archived repos reject push mirrors)
- restore_to_primary.sh: add require_vars for Fedora SSH variables

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/common.sh

@@ -303,14 +303,20 @@ github_api() {
 # ---------------------------------------------------------------------------
 
 render_template() {
-  local src="$1" dest="$2"
+  local src="$1" dest="$2" vars="${3:-}"
 
   if [[ ! -f "$src" ]]; then
     log_error "Template not found: $src"
     return 1
   fi
 
-  envsubst < "$src" > "$dest"
+  if [[ -z "$vars" ]]; then
+    log_error "render_template requires an explicit variable list (third argument)"
+    log_error "Example: render_template src dest '\${VAR1} \${VAR2}'"
+    return 1
+  fi
+
+  envsubst "$vars" < "$src" > "$dest"
 }
 
 # ---------------------------------------------------------------------------