CE-WP-0006/0007: Capture view polish, workplans, and UX refinements

- Blob URL stability, scroll centre, strip-only visual guide
- Focus-gated linking, unlink clears overlay, field badge tooltips
- Capture layout (viewer centre), grey guide lines, Add field button
- Workplans CE-WP-0006 (done) and CE-WP-0007 (T01-T09 done, T10-T12 todo)
- Integration tests and viewer-url helpers

src/binder/state/active.ts

@@ -54,6 +54,7 @@ type Action =
       evidenceItemId: EvidenceItemId;
       annotationId: AnnotationId | null;
     }
+  | { type: "clear-active-evidence" }
   | { type: "clear" };
 
 function reducer(state: ActiveState, action: Action): ActiveState {
@@ -78,6 +79,12 @@ function reducer(state: ActiveState, action: Action): ActiveState {
         activeEvidenceItemId: action.evidenceItemId,
         activeAnnotationId: action.annotationId,
       };
+    case "clear-active-evidence":
+      return {
+        activeTarget: state.activeTarget,
+        activeEvidenceItemId: null,
+        activeAnnotationId: null,
+      };
     case "clear":
       return EMPTY_ACTIVE_STATE;
   }
@@ -90,6 +97,7 @@ export interface ActiveStateApi {
     evidenceItemId: EvidenceItemId,
     annotationId?: AnnotationId | null,
   ): void;
+  clearActiveEvidence(): void;
   clear(): void;
 }
 
@@ -144,13 +152,17 @@ export function ActiveStateProvider(props: ActiveStateProviderProps) {
     [props.bus],
   );
 
+  const clearActiveEvidence = useCallback(() => {
+    dispatch({ type: "clear-active-evidence" });
+  }, []);
+
   const clear = useCallback(() => {
     dispatch({ type: "clear" });
   }, []);
 
   const value = useMemo<ActiveStateApi>(
-    () => ({ state, focusTarget, setActiveEvidence, clear }),
-    [state, focusTarget, setActiveEvidence, clear],
+    () => ({ state, focusTarget, setActiveEvidence, clearActiveEvidence, clear }),
+    [state, focusTarget, setActiveEvidence, clearActiveEvidence, clear],
   );
 
   return createElement(ActiveStateContext.Provider, { value }, props.children);