feat(playground): add UI components, MCP tools, and header link

Playground UI (SolidJS + Three.js + CodeMirror 6):
- PlaygroundCanvas: reactive WebGL renderer with preserveDrawingBuffer,
  error extraction via getShaderInfoLog, auto screenshot capture
- PlaygroundEditor: CodeMirror 6 with C++ syntax (GLSL-compatible),
  one-dark theme, external value sync without cursor loss
- PlaygroundLayout: split editor/canvas layout, SSE connection for
  agent-driven updates, debounced manual edits, error display bar
- /playground route with ?session= param, auto-creates new session

MCP playground tools (4 new tools):
- create_playground: creates session, returns URL
- update_shader: updates GLSL, returns errors + screenshot as image content
- get_preview: returns latest screenshot as MCP image content
- get_errors: returns compilation error list
- Handlers with dependency-injected fetch for testability
- 8 handler tests (all passing)

Polish:
- Added "playground" link to Header navigation
- Updated existing MCP tests for 7 tools (was 3)
- All tests pass across 13 test files

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

Author: devallibus

apps/web/bun.lock

@@ -12,6 +12,10 @@
   },
   "dependencies": {
     "@ai-sdk/anthropic": "^3.0.58",
+    "@codemirror/lang-cpp": "^6.0.3",
+    "@codemirror/state": "^6.5.4",
+    "@codemirror/theme-one-dark": "^6.1.3",
+    "@codemirror/view": "^6.39.16",
     "@fontsource/geist-mono": "^5.2.7",
     "@fontsource/geist-sans": "^5.2.5",
     "@tailwindcss/vite": "^4.1.18",
@@ -22,6 +26,7 @@
     "@tanstack/solid-start": "latest",
     "ai": "^6.0.116",
     "better-auth": "^1.5.4",
+    "codemirror": "^6.0.2",
     "nitro": "npm:nitro-nightly@latest",
     "solid-js": "^1.9.11",
     "tailwindcss": "^4.1.18",

apps/web/package.json

@@ -20,6 +20,13 @@ export default function Header() {
           >
             shaders
           </Link>
+          <Link
+            to="/playground"
+            class="text-text-muted no-underline transition hover:text-text-primary"
+            activeProps={{ class: 'text-text-primary' }}
+          >
+            playground
+          </Link>
           <Link
             to="/about"
             class="text-text-muted no-underline transition hover:text-text-primary"