feat(webbrowser): add storage_state support to reuse authenticated Playwright sessions

[fede03billy]

This PR lets proxy-lite load an existing Playwright storage_state file (cookies + local/sessionStorage) so agents can start from an already-authenticated context instead of repeating the login flow.

Example:

from proxy_lite import Runner, RunnerConfig

cfg = RunnerConfig.from_dict({
    "environment": {
        "name": "webbrowser",
        "homepage": "https://www.giponext.it/Agende/Classic",
        "headless": False,
        # NEW: point to the JSON produced by playwright.storage_state()
        "storage_state": "/abs/path/to/state.json",
    },
    "solver": {
        "name": "simple",
        "agent": {
            "name": "proxy_lite",
            "client": { "name": "convergence" }
        },
    },
})
runner = Runner(config=cfg)