feat: add visual review workflow for automated PR screenshot comparison

Adds a label-triggered GitHub Actions workflow that automatically generates
before/after screenshots when web UI changes are made in a PR. Uses smart
dependency analysis to only screenshot pages affected by the changed files.

Key components:
- Reverse dependency analyzer: traces changed files through the import graph
  to find which +page.svelte routes are affected
- Screenshot scenarios: Playwright tests using existing mock-network infrastructure
  (no Docker/backend needed) for fast, deterministic screenshots
- Pixel comparison: generates diff images highlighting changed pixels
- GitHub Actions workflow: triggered by 'visual-review' label, posts results
  as a PR comment with change percentages per page

https://claude.ai/code/session_01XSTqDJXuR4jaLN7SGm3uES

e2e/package.json

@@ -18,7 +18,10 @@
     "format:fix": "prettier --write .",
     "lint": "eslint \"src/**/*.ts\" --max-warnings 0",
     "lint:fix": "pnpm run lint --fix",
-    "check": "tsc --noEmit"
+    "check": "tsc --noEmit",
+    "screenshots": "pnpm exec playwright test --config playwright.screenshot.config.ts",
+    "screenshots:compare": "npx tsx src/screenshots/compare.ts",
+    "screenshots:analyze": "npx tsx src/screenshots/analyze-deps.ts"
   },
   "keywords": [],
   "author": "",