Drop Renovate and add a built-entrypoint render test

[P-Theo]

Summary

• Delete renovate.jsonc. It never produced a run — no Dependency Dashboard, PRs, or renovate/* branches — and the pinned betas are bumped by hand with fixes.
• README: keep only the earliest known compatible beta (0.0.0-beta-17595) and point at the issue tracker; drop the "latest tested beta" claim that moved several times a day.
• check-compatibility.mjs: drop the assertion that the README matches the pinned version, which no longer has a phrase to match. The version-format, package lockstep, CLI-version, and CI GitHub-release checks stay.
• Add artifact-level render coverage: bunfig.toml preloads @opentui/solid/preload, and entrypoint.test.tsx builds dist/tui.js with the production script, imports it, registers the compiled plugin with a fake host context, and renders the composer claim through testRender while driving the plugin's own refresh timer manually. It asserts the live label through text, reasoning, and tool-input streaming; exact settlement and freeze; reset on a new run; and independent orchestrator/sub-agent sessions.
• docs/development.md documents the test setup; tsconfig.json includes the new test.

No runtime behavior changes.

Verification

• npm run check:compatibility
• npm run lint — 0 warnings, 0 errors
• npm run check
• npm test — 61 pass, 0 fail
• npm run build