feat: rework runner config to INI format with full field support

Replace pipe-delimited runners.conf with INI-style sections supporting
host resolution, container images, repo-scoped tokens, resource limits,
capacity, and SSH key passthrough. All defaults pulled from .env.

- Add INI parsing helpers (ini_list_sections, ini_get, ini_set) to common.sh
- Add SSH key support (UNRAID_SSH_KEY, FEDORA_SSH_KEY) to ssh_exec/scp_to
- Add .env vars: RUNNER_DEFAULT_IMAGE, RUNNER_DEFAULT_CAPACITY,
  RUNNER_DEFAULT_DATA_PATH, LOCAL_RUNNER_DATA_PATH, LOCAL_REGISTRY
- Rewrite manage_runner.sh with host/image/token resolution and resource limits
- Rewrite configure_runners.sh wizard for INI format with all 9 fields
- Update phase3 scripts to use ini_list_sections instead of pipe parsing
- Add runners.conf INI validation to preflight.sh (check 5b)
- Update templates to use resolved labels, capacity, and deploy resources

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

phase3_teardown.sh

@@ -31,15 +31,11 @@ fi
 printf 'This will stop and remove all runners. Continue? [y/N] '
 read -r confirm
 if [[ "$confirm" =~ ^[Yy]$ ]]; then
-  while IFS='|' read -r name rest; do
-    # Skip comments and blank lines
-    [[ "$name" =~ ^[[:space:]]*# ]] && continue
+  while IFS= read -r name; do
     [[ -z "$name" ]] && continue
-
-    name=$(echo "$name" | xargs)
     log_info "Removing runner: ${name}"
     "${SCRIPT_DIR}/manage_runner.sh" remove --name "$name" || true
-  done < "$RUNNERS_CONF"
+  done < <(ini_list_sections "$RUNNERS_CONF")
   log_success "All runners removed"
 else
   log_info "Skipped runner removal"