Refactor Playwright component tests around SQL fixtures

[lovasoa]

Summary

• add a shared Playwright harness that opens each suite's SQL fixture, checks response/render errors, waits for component initialization, and reports uncaught page errors
• move chart and map behavior tests to deterministic fixtures/<suite>/{index.sql,test.ts} applications rendered through SQLPage instead of injecting synthetic DOM or calling private initializers
• separate fixture and official-site Playwright projects, start the fixture server locally and in CI, and document the convention in CONTRIBUTING.md and AGENTS.md
• use configured baseURL values for the remaining official-site smoke tests

Why

This follows Playwright's recommendations to test user-visible behavior, isolate tests, use locators and web-first assertions, and avoid timing-based waits. It also exercises SQLPage's real SQL-to-template-to-initialization path, so component tests cannot silently drift from production markup.

The diff is +42 lines overall. The small increase buys explicit SQL applications, server configuration, automatic health/error checks, and contributor documentation; the chart suite itself is shorter, and the map suite replaces a fixed 500 ms sleep with deterministic outcome waits.

Validation

• npm run format
• npm test
• npm run test in tests/end-to-end (70 passed)
• CI=1 npx playwright test --project=fixtures --reporter=line (40 passed, one worker)

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