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>

phase5_migrate_pipelines.sh

@@ -113,15 +113,15 @@ for repo in "${REPOS[@]}"; do
     cat "$dest" >> "$tmpwf"
     mv "$tmpwf" "$dest"
 
-    # Replace GitHub-specific context variables with Gitea equivalents
-    # Using sed with a temp file for portability (macOS sed -i requires '',
-    # GNU sed -i requires no arg — avoiding both by writing to a temp file)
+    # Replace GitHub-specific context variables with Gitea equivalents.
+    # Only match inside ${{ ... }} expression delimiters to avoid mangling
+    # URLs, comments, or other strings that happen to contain "github.".
+    # Two patterns: with spaces (${{ github.X }}) and without (${{github.X}}).
+    # Character class [a-z_.] covers nested contexts like github.event.pull_request.number.
     tmpwf=$(mktemp)
     sed \
-      -e 's/github\.repository/gitea.repository/g' \
-      -e 's/github\.event/gitea.event/g' \
-      -e 's/github\.token/gitea.token/g' \
-      -e 's/github\.server_url/gitea.server_url/g' \
+      -e 's/\${{ github\.\([a-z_.]*\) }}/\${{ gitea.\1 }}/g' \
+      -e 's/\${{github\.\([a-z_.]*\)}}/\${{gitea.\1}}/g' \
       "$dest" > "$tmpwf"
     mv "$tmpwf" "$dest"