Phase D: cross-runtime tweaks (visual-companion, executing-plans, test)

Misc platform/runtime statements and adjacencies that don't fit the
prose, config-ref, README-ordering, or tool-vocabulary buckets:

- visual-companion frame template: rename CSS/HTML id #claude-content
  → #frame-content. The id is purely styling — nothing external
  references it. The brainstorm-server test that asserted the old
  string is updated in lockstep.

- visual-companion launch instructions: add a Copilot CLI section
  alongside Claude Code, Codex, and Gemini CLI; combine the Claude
  Code (macOS / Linux) and (Windows) sections so heading style
  matches the other (non-OS-qualified) platforms.

- visual-companion: "Use Write tool" → "Use your file-creation tool"
  for the cat/heredoc warning. The prohibition is what's load-
  bearing, not the tool name.

- executing-plans/SKILL.md: list all subagent-capable runtimes
  (Claude Code, Codex CLI, Codex App, Copilot CLI, Gemini CLI) and
  point at the per-platform tool refs as the source of truth.

- executing-plans/SKILL.md: relative path "using-superpowers/
  references/" → "../using-superpowers/references/" to resolve
  correctly from the executing-plans/ directory.

No bundled spec doc here — Phase D was scope-extension work that
took place across rounds, with no standalone spec authored.

skills/brainstorming/scripts/frame-template.html

@@ -13,7 +13,7 @@
      * - Scrollable main content area
      * - CSS helpers for common UI patterns
      *
-     * Content is injected via placeholder comment in #claude-content.
+     * Content is injected via placeholder comment in #frame-content.
      */
 
     * { box-sizing: border-box; margin: 0; padding: 0; }
@@ -77,7 +77,7 @@
     .header .status::before { content: ''; width: 6px; height: 6px; background: var(--success); border-radius: 50%; }
 
     .main { flex: 1; overflow-y: auto; }
-    #claude-content { padding: 2rem; min-height: 100%; }
+    #frame-content { padding: 2rem; min-height: 100%; }
 
     .indicator-bar {
       background: var(--bg-secondary);
@@ -201,7 +201,7 @@
   </div>
 
   <div class="main">
-    <div id="claude-content">
+    <div id="frame-content">
       <!-- CONTENT -->
     </div>
   </div>