test(web): cover user-only skill invocation end to end

The policy scenario now expects the user-only quadrant in the menu with
its marker (riding the description — the hint field is claim-state ghost
text, which the menu never renders), and a new skill-user-invoke scenario
drives /name args through the composer against the real host: the claim
lands skill.invoke, the transcript shows the dedicated card with the
collapsed <skill_content> body, and a paced replay answers the injected
turn deterministically.

apps/web/tests/snapshots/skill-invocation-policy/menu.expected.md

@@ -1,3 +1,4 @@
 - listbox "Trigger suggestions":
   - text: Skills
   - option "policy-shared Available to both model and user invocation" [selected]
+  - option "policy-user-only user-only · Available only to user invocation"

apps/web/tests/snapshots/skill-user-invoke/ui.expected.md

@@ -0,0 +1,31 @@
+- banner:
+  - navigation "Session hierarchy":
+    - button "workspace" [disabled]
+  - tablist:
+    - tab "Chat" [selected]
+    - tab "Trajectory"
+- text: /user-invoke-demo and confirm the fixture wiring
+- group: View injected skill content
+- text: {{clock}}
+- button "Copy":
+  - img
+- button "Context injection @deepseek-ai/dsh-system-prompt":
+  - img
+  - img
+  - text: Context injection @deepseek-ai/dsh-system-prompt
+- paragraph: USER_INVOKE_REPLY acknowledged; following the injected skill.
+- button "Copy":
+  - img
+- button "Branch into a new conversation":
+  - img
+- text: {{clock}} Ran for {{duration}} TTFT {{duration}} {{throughput}} tok/s
+- textbox "Message the agent"
+- button "Commands":
+  - img
+- 'button "Access mode, current: Workspace Write"': Workspace Write
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
+  - img
+- button "0% of context used"
+- button "Send message" [disabled]
+- text: 1 turns · 1 steps LLM {{duration}} TTFT avg {{duration}} · {{throughput}} tok/s Cache hit 0% Input 256 tok · Output 16 tok