docs: restructure brainstorming skill with progressive disclosure

SKILL.md is now minimal: process, principles, and a prompt that notes
the visual companion is new/token-intensive/slow. All visual companion
details move to visual-companion.md as a progressive disclosure document
read only when the user opts in.

Delete CLAUDE-INSTRUCTIONS.md (content folded into visual-companion.md).
Document fragment vs full-document behavior and --project-dir persistence.

skills/brainstorming/SKILL.md

@@ -5,8 +5,6 @@ description: "You MUST use this before any creative work - creating features, bu
 
 # Brainstorming Ideas Into Designs
 
-## Overview
-
 Help turn ideas into fully formed designs and specs through natural collaborative dialogue.
 
 Start by understanding the current project context, then ask questions one at a time to refine the idea. Once you understand what you're building, present the design and get user approval.
@@ -86,16 +84,8 @@ digraph brainstorming {
 **Spec Review Loop:**
 After writing the spec document:
 1. Dispatch spec-document-reviewer subagent (see spec-document-reviewer-prompt.md)
-2. If ❌ Issues Found:
-   - Fix the issues in the spec document
-   - Re-dispatch reviewer
-   - Repeat until ✅ Approved
-3. If ✅ Approved: proceed to implementation setup
-
-**Review loop guidance:**
-- Same agent that wrote the spec fixes it (preserves context)
-- If loop exceeds 5 iterations, surface to human for guidance
-- Reviewers are advisory - explain disagreements if you believe feedback is incorrect
+2. If Issues Found: fix, re-dispatch, repeat until Approved
+3. If loop exceeds 5 iterations, surface to human for guidance
 
 **Implementation:**
 - Invoke the writing-plans skill to create a detailed implementation plan
@@ -112,83 +102,10 @@ After writing the spec document:
 
 ## Visual Companion (Claude Code Only)
 
-A browser-based visual companion for showing mockups, diagrams, and options. Use it whenever visual representation makes feedback easier. **Only works in Claude Code.**
+A browser-based visual companion for showing mockups, diagrams, and options during brainstorming. Use it whenever visual representation would make feedback easier than text descriptions alone.
 
-### When to Use
+**When the topic involves visual decisions, ask:**
+> "This involves some visual decisions. I can show mockups in a browser window so you can see options and give feedback visually. This feature is still new — it can be token-intensive and a bit slow, but it works well for layout, design, and architecture questions. Want to try it? (Requires opening a local URL)"
 
-Use the visual companion when seeing beats describing:
-- **UI mockups** - layouts, navigation, component designs
-- **Architecture diagrams** - system components, data flow, relationships
-- **Complex choices** - multi-option decisions with visual trade-offs
-- **Design polish** - when the question is about look and feel
-- **Spatial relationships** - file structures, database schemas, state machines
-
-**Always ask first:**
-> "This involves some visual decisions. Would you like me to show mockups in a browser window? (Requires opening a local URL)"
-
-Only proceed if they agree. Otherwise, describe options in text.
-
-### How to Use Effectively
-
-**Scale fidelity to the question.** If you're asking about layout structure, simple wireframes suffice. If you're asking about visual polish, show polish. Match the mockup's detail level to what you're trying to learn.
-
-**Explain the question on each page.** Don't just show options—state what decision you're seeking. "Which layout feels more professional?" not just "Pick one."
-
-**Iterate before moving on.** If feedback changes the current screen, update it and show again. Validate that your changes address their feedback before proceeding to the next question.
-
-**Limit choices to 2-4 options.** More gets overwhelming. If you have more alternatives, narrow them down first or group them.
-
-**Use real content when it matters.** For a photography portfolio, use actual images (Unsplash). For a blog, use realistic text. Placeholder content obscures design issues.
-
-### Starting a Session
-
-```bash
-# Start server (creates unique session directory)
-${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/start-server.sh
-
-# Returns: {"type":"server-started","port":52341,"url":"http://localhost:52341",
-#           "screen_dir":"/tmp/brainstorm-12345"}
-```
-
-Save `screen_dir` from the response. Tell user to open the URL.
-
-### The Loop
-
-1. **Start watcher first** (background bash) - avoids race condition:
-   ```bash
-   ${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/wait-for-feedback.sh $SCREEN_DIR
-   ```
-
-2. **Write HTML** to a new file in `screen_dir`:
-   - Use semantic filenames: `platform.html`, `visual-style.html`, `layout.html`
-   - **Never reuse filenames** - each screen gets a fresh file
-   - Use Write tool - **never use cat/heredoc** (dumps noise into terminal)
-   - Server automatically serves the newest file
-
-3. **Tell user what to expect:**
-   - Remind them of the URL (every step, not just first)
-   - Give a brief text summary of what's on screen (e.g., "Showing 3 layout options for the homepage")
-   - This lets them know what to look for before switching to browser
-
-4. **Wait for feedback** - call `TaskOutput(task_id, block=true, timeout=600000)`
-   - If timeout, call TaskOutput again (watcher still running)
-   - After 3 timeouts (30 min), say "Let me know when you want to continue"
-
-5. **Process feedback** - returns JSON like `{"choice": "a", "feedback": "make header smaller"}`
-
-6. **Iterate or advance** - if feedback changes current screen, write a new file (e.g., `layout-v2.html`). Only move to next question when current step is validated.
-
-7. Repeat until done.
-
-### Cleaning Up
-
-```bash
-${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/stop-server.sh $SCREEN_DIR
-```
-
-### Resources
-
-- Frame template: `${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/frame-template.html`
-- CSS classes: `.options`, `.cards`, `.mockup`, `.split`, `.pros-cons`
-- Detailed examples: `${CLAUDE_PLUGIN_ROOT}/lib/brainstorm-server/CLAUDE-INSTRUCTIONS.md`
-- Quick reference: `${CLAUDE_PLUGIN_ROOT}/skills/brainstorming/visual-companion.md`
+If they agree, read the detailed guide before proceeding:
+`${CLAUDE_PLUGIN_ROOT}/skills/brainstorming/visual-companion.md`