feat(tools): add a browser.cdpUrl setting for the default automation target

Attaching to a long-running browser (a signed-in profile, an Electron app kept
open for a session) meant repeating app.cdp_url on every browser call, and any
call that omitted it silently launched a fresh headless Chromium instead.

browser.cdpUrl supplies that endpoint once. It is a default rather than an
override: app.cdp_url and app.path still win, and an unset or blank value leaves
cmux and headless resolution exactly as before.

packages/coding-agent/src/tools/browser.ts

@@ -95,6 +95,11 @@ function resolveBrowserKind(params: BrowserParams, session: ToolSession): Browse
 		const exe = resolveToCwd(app.path, session.cwd);
 		return { kind: "spawned", path: exe };
 	}
+	// A configured endpoint is a default, not an override: explicit app options win.
+	const configuredCdpUrl = (session.settings.get("browser.cdpUrl") as string | undefined)?.trim();
+	if (configuredCdpUrl) {
+		return { kind: "connected", cdpUrl: configuredCdpUrl.replace(/\/+$/, "") };
+	}
 	const cmuxKind = resolveCmuxKind({
 		settingEnabled: session.settings.get("browser.cmux") as boolean | undefined,
 	});