feat(qa): add Playwright MCP test agents & config

Introduces Playwright testing agents (planner, generator, healer) powered by MCP to plan, generate, and heal end-to-end tests.

Configures the MCP server and integrates agent workflows into OpenCode and GitHub chat modes to enable AI-assisted testing.

Adds Playwright test dependency and updates lockfile; adjusts markdown lint ignores to reduce noise.

Adds contributor guidance for Claude Code to streamline local development.

Normalizes shell script shebangs to use /usr/bin/env bash for portability.

Enables automated browser testing workflows and resilient test maintenance within AI-enabled tooling.

package.json

@@ -6,7 +6,7 @@
     "lint:js": "oxlint",
     "lint:js:fix": "bun lint:js -- --fix",
     "lint:js:strict": "oxlint --import-plugin -D correctness -W suspicious",
-    "lint:md": "markdownlint-cli2 \"**/*.md\" \"#node_modules\" \"#.{node_modules,trunk,grit,venv}\"",
+    "lint:md": "markdownlint-cli2 \"**/*.md\" \"#node_modules\" \"#.{node_modules,trunk,grit,venv,opencode,github/chatmodes,claude/agents}\"",
     "lint:md:fix": "bun lint:md -- --fix",
     "lint:py": "uvx ruff check",
     "lint:py:fix": "uvx ruff check --fix",
@@ -15,6 +15,7 @@
     "typecheck:py": "uvx ty check"
   },
   "devDependencies": {
+    "@playwright/test": "^1.56.1",
     "markdownlint-cli2": "^0.18.1",
     "oxlint": "^1.25.0",
     "oxlint-tsgolint": "^0.5.0",