build(web): replace Playwright MCP with project-scoped Playwright CLI

- feat: add `.agents/skills/playwright-cli/` with complete Skill
  markdown, agent interface, and 9 reference files covering session
  management, spec-driven testing, video recording, tracing, storage,
  request mocking, element attributes, test debugging, and running
  custom code
- feat: add `.playwright/cli.config.json` to configure the Playwright
  CLI
- feat: add `web/package.json` `playwright:cli` script that resolves
  `playwright cli` from the repo root
- build: remove `@playwright/mcp` dependency from `web/package.json`
- build: set `XDG_CACHE_HOME` in `mise.toml`
- build: delete `.codex/config.toml` (MCP server config)
- docs: update `README.md`, `docs/web/roadmap.md`,
  `docs/web/decisions.md`, and `web/README.md` to reflect the new
  Playwright CLI approach

.agents/skills/playwright-cli/references/element-attributes.md

@@ -0,0 +1,23 @@
+# Inspecting Element Attributes
+
+When the snapshot doesn't show an element's `id`, `class`, `data-*` attributes, or other DOM properties, use `eval` to inspect them.
+
+## Examples
+
+```bash
+mise exec -- npm run playwright:cli -- snapshot
+# snapshot shows a button as e7 but doesn't reveal its id or data attributes
+
+# get the element's id
+mise exec -- npm run playwright:cli -- eval "el => el.id" e7
+
+# get all CSS classes
+mise exec -- npm run playwright:cli -- eval "el => el.className" e7
+
+# get a specific attribute
+mise exec -- npm run playwright:cli -- eval "el => el.getAttribute('data-testid')" e7
+mise exec -- npm run playwright:cli -- eval "el => el.getAttribute('aria-label')" e7
+
+# get a computed style property
+mise exec -- npm run playwright:cli -- eval "el => getComputedStyle(el).display" e7
+```