CI no longer exercises a tui-less core install (every job syncs --extra tui) #20

Location: .github/workflows/ci.yml:61

The previous workflow ran the suite against uv sync --extra dev (no tui extra). Every new job (lint, typecheck, test, security) syncs --extra dev --extra tui.

Failure scenario: if a core module (server.py, __main__.py) gains an accidental top-level import of textual/selectolax (e.g. via from .fetch import ... or from .tui import ...), plain pip install perplexity-agent users get ImportError at server startup while CI stays green. The _run_tui missing-extra error path is also never exercised against a real core env.

Suggested fix: keep one matrix leg (or a dedicated job) on uv sync --extra dev only.

Found by /code-review (high effort).