feat(emulate): add mobile device emulation via CDP Emulation domain (#60)

* feat(emulate): add mobile device emulation via CDP Emulation domain

Add `bsk emulate` so agents can debug mobile page behaviour by
emulating a device environment on a session tab:

- Viewport metrics (Emulation.setDeviceMetricsOverride), User-Agent
  (Emulation.setUserAgentOverride, optional accept-language and UA
  client-hints metadata), and touch (Emulation.setTouchEmulationEnabled
  with maxTouchPoints).
- Seven CLI-side device presets (iphone-14, iphone-14-pro-max,
  iphone-se, pixel-7, galaxy-s23, ipad-mini, galaxy-tab-s8) via
  --device; manual flags (--width/--height/--dpr/--mobile/--ua/
  --accept-language/--touch/--max-touch-points) work standalone or
  override individual preset fields.
- `bsk emulate --off` clears every override (clearDeviceMetricsOverride
  + touch disabled + empty UA override) and restores the real
  environment.
- Overrides are per-tab (CDP per-target) and not inherited by new tabs;
  the result JSON carries a note reminding agents to re-apply.

Wire: new tool.emulate method end-to-end (bsk-protocol types + JSON
schemas + Method::ToolEmulate classified BrowserMutation, daemon
forwarding, CLI subcommand, extension tool handler + ChromiumCdp
Emulation wrappers, dispatcher registration), docs in both SKILL.md
copies, and unit tests on every layer.

* refine(emulate): merge per-tab state and align preset override semantics

- extension: remember the applied emulation state per tab and merge each new request onto it field by field before applying, so a later --width/--height no longer resets an earlier preset's dpr/mobile; --off clears the stored state along with the CDP overrides
- extension: cdp_failed errors now note that already-applied overrides were not rolled back and can be reset with --off
- cli: validate width/height pairing and metric requirements on the merged preset+flags result, so --device iphone-14 --width 500 keeps the preset height
- cli: add --no-mobile/--no-touch (conflicting with --mobile/--touch) to turn preset mobile/touch fields back off
- docs: describe the merge behaviour, --no-mobile/--no-touch and --off state clearing in both SKILL.md copies

crates/bsk-cli/tests/cli_parse.rs

@@ -323,3 +323,162 @@ fn rejects_invalid_window_resize_dimensions() {
     // width/height are required for resize.
     assert!(Cli::try_parse_from(["bsk", "window", "resize", "--session", "s1"]).is_err());
 }
+
+#[test]
+fn parses_emulate_with_device_preset() {
+    use bsk::cli::emulate::EmulateArgs;
+    let cli = parse(&["bsk", "emulate", "--session", "s1", "--device", "iphone-14"]);
+    let Command::Emulate(EmulateArgs {
+        session,
+        device,
+        off,
+        ..
+    }) = cli.command
+    else {
+        panic!("expected emulate subcommand");
+    };
+    assert_eq!(session, "s1");
+    assert_eq!(device.as_deref(), Some("iphone-14"));
+    assert!(!off);
+}
+
+#[test]
+fn parses_emulate_manual_overrides() {
+    let cli = parse(&[
+        "bsk",
+        "emulate",
+        "--session",
+        "s1",
+        "--width",
+        "390",
+        "--height",
+        "844",
+        "--dpr",
+        "3",
+        "--mobile",
+        "--ua",
+        "Mozilla/5.0 (iPhone)",
+        "--accept-language",
+        "zh-CN",
+        "--touch",
+        "--max-touch-points",
+        "5",
+        "--tab-id",
+        "7",
+    ]);
+    let Command::Emulate(args) = cli.command else {
+        panic!("expected emulate subcommand");
+    };
+    assert_eq!(args.width, Some(390));
+    assert_eq!(args.height, Some(844));
+    assert_eq!(args.dpr, Some(3.0));
+    assert!(args.mobile);
+    assert_eq!(args.ua.as_deref(), Some("Mozilla/5.0 (iPhone)"));
+    assert_eq!(args.accept_language.as_deref(), Some("zh-CN"));
+    assert!(args.touch);
+    assert_eq!(args.max_touch_points, Some(5));
+    assert_eq!(args.tab_id, Some(7));
+}
+
+#[test]
+fn parses_emulate_off() {
+    let cli = parse(&["bsk", "emulate", "--session", "s1", "--off"]);
+    let Command::Emulate(args) = cli.command else {
+        panic!("expected emulate subcommand");
+    };
+    assert!(args.off);
+}
+
+#[test]
+fn parses_emulate_no_mobile_no_touch() {
+    let cli = parse(&[
+        "bsk",
+        "emulate",
+        "--session",
+        "s1",
+        "--device",
+        "iphone-14",
+        "--no-mobile",
+        "--no-touch",
+    ]);
+    let Command::Emulate(args) = cli.command else {
+        panic!("expected emulate subcommand");
+    };
+    assert!(args.no_mobile);
+    assert!(args.no_touch);
+    assert!(!args.mobile);
+    assert!(!args.touch);
+}
+
+#[test]
+fn rejects_conflicting_emulate_flags() {
+    for extra in [
+        &["--mobile", "--no-mobile"][..],
+        &["--touch", "--no-touch"][..],
+    ] {
+        let mut argv = vec!["bsk", "emulate", "--session", "s1", "--device", "iphone-14"];
+        argv.extend_from_slice(extra);
+        assert!(Cli::try_parse_from(argv).is_err());
+    }
+}
+
+#[test]
+fn rejects_invalid_emulate_values() {
+    // Zero / out-of-range dimensions.
+    assert!(
+        Cli::try_parse_from([
+            "bsk",
+            "emulate",
+            "--session",
+            "s1",
+            "--width",
+            "0",
+            "--height",
+            "844"
+        ])
+        .is_err()
+    );
+    // Non-positive dpr.
+    assert!(
+        Cli::try_parse_from([
+            "bsk",
+            "emulate",
+            "--session",
+            "s1",
+            "--width",
+            "390",
+            "--height",
+            "844",
+            "--dpr",
+            "0"
+        ])
+        .is_err()
+    );
+    assert!(
+        Cli::try_parse_from([
+            "bsk",
+            "emulate",
+            "--session",
+            "s1",
+            "--width",
+            "390",
+            "--height",
+            "844",
+            "--dpr",
+            "abc"
+        ])
+        .is_err()
+    );
+    // Zero touch points.
+    assert!(
+        Cli::try_parse_from([
+            "bsk",
+            "emulate",
+            "--session",
+            "s1",
+            "--max-touch-points",
+            "0"
+        ])
+        .is_err()
+    );
+}