chore: silence unused import/variable/dead-code warnings (#101) (#126)

- obscura-net/cookies.rs: #[allow(dead_code)] on CookieEntry.same_site
  (parsed today, kept for future SameSite enforcement).
- obscura-js/runtime.rs: drop vestigial BOOTSTRAP_JS const; bootstrap.js
  is already embedded into the V8 snapshot via build.rs.
- obscura-js/ops.rs: prefix the four unused fields in
  InterceptResolution::Continue with _.
- obscura-cdp/dispatch.rs: drop unused InterceptResolution import.
- obscura-cdp/domains/fetch.rs: drop unused Arc / Mutex / CdpEvent imports.
- obscura-cdp/domains/input.rs: prefix _button / _click_count; CDP
  parses them but the JS click stub is hardcoded for now.
- obscura-cdp/server.rs: prefix _processor_handle and _ctx; drop dead
  initial Ok(())/None for navigate_result/page_back - they are
  unconditionally overwritten in the only loop break arm.

cargo build --workspace: 0 warnings.
cargo test --workspace: 113 passed.

crates/obscura-js/src/ops.rs

@@ -376,7 +376,7 @@ async fn op_fetch_url(
                         "error": reason,
                     }).to_string());
                 }
-                Ok(InterceptResolution::Continue { url: new_url, method: new_method, headers: new_headers, body: new_body }) => {
+                Ok(InterceptResolution::Continue { url: _new_url, method: _new_method, headers: _new_headers, body: _new_body }) => {
                     tracing::debug!("Interception: continue request {}", url);
                 }
                 Err(_) => {