Add method-role overlay experiment on basic-webserver

[koliyo]

Summary

• Exploratory hybrid: routes in Roc, markup in Ui.rocci. experiments/rocci-web overlays basic-webserver 0.16.0 (same tarball as dispatch.rs) and exposes pf.Rocci wraps. The gallery pf is "../rocci-web/vendor/main.roc". Run ./experiments/rocci-web/fetch-bws.sh first (vendor/ is gitignored).
• App still matches (method, path) and calls wraps. Command empty-SSE vs 204 needs Rocci.command!(request.headers()) from main.roc; request.headers() in another module crashes this nightly.
• A two-route List of Rocci.view / Rocci.fragment linked, then crashed at runtime (dispatch on a value that can never exist). requires { routes } does not typecheck. Hosted register needs a rebuilt libhost.a (not in this overlay).
• Not a cutover from @method:role, not a generated-dispatch change, not an SSE-idle fork, not a shipped host. Knowledge: opinionated BWS overlay.

Test plan

• ./experiments/rocci-web/fetch-bws.sh
• cargo run -q -p rocci-cli -- run experiments/method-role-lib --no-window
• GET / returns HTML; POST /actions/counter/increment is one datastar-patch-elements event
• POST /actions/live/increment is 204 without Datastar-Request and empty SSE with it
• GET /sse stays open; GET /actions/tabs/1 is a fragment; compose returns patch-elements and patch-signals
• GET /actions/search/results?q=live filters; GET /health is ok; GET /counter/ is 308
• cargo run -q -p rocci-okf -- check knowledge --profile rocci --format terminal