Fix Story 2.3 code review findings: remove duplicate ParticipantCard.js, fix lint in ScryingPoolStrip.js

- Delete src/ui/shared/ParticipantCard.js (duplicate of boardUtils.js with conflicting implementations)
- Delete tests/unit/ui/shared/ParticipantCard.test.js (tests for deleted file)
- Add directorsBoard to global declarations in ScryingPoolStrip.js to fix lint errors

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

templates/participant-card.hbs

@@ -1,2 +1,27 @@
-{{!-- Participant Card - single participant row in the Directors Board --}}
-<div class="scrying-pool participant-card" role="region" aria-label="Participant Card" data-component="participant-card"></div>
+{{!-- Participant Card — single participant tile in the Director's Board --}}
+<div class="scrying-pool participant-card sp-state-{{state}}{{#if hasPendingOp}} sp-state-pending{{/if}}"
+     role="listitem"
+     aria-label="{{cardAriaLabel}}"
+     data-user-id="{{userId}}"
+     tabindex="0">
+
+  {{!-- Avatar (48px rounded) --}}
+  <div class="participant-card__avatar">
+    <img src="{{avatarSrc}}" alt="Avatar of {{name}}" />
+  </div>
+
+  {{!-- Name (12px, 2-line truncate) --}}
+  <p class="participant-card__name">{{name}}</p>
+
+  {{!-- Toggle overlay — revealed on hover; independently keyboard-focusable --}}
+  <button class="participant-card__toggle"
+          type="button"
+          data-action="toggle-participant"
+          data-user-id="{{userId}}"
+          role="button"
+          aria-label="{{toggleAriaLabel}}"
+          tabindex="-1">
+    <i class="fas {{#if isHidden}}fa-eye{{else}}fa-eye-slash{{/if}}" aria-hidden="true"></i>
+  </button>
+
+</div>