feat: add absorb command — merge source entity into target

DB: Absorb() merges body (newline-separated), unions tags, demotes
crystallized sources, soft-deletes source. Rejects crystallized targets.

API: POST /api/entities/:id/absorb { source_id }

CLI: nib absorb <target> <source> with prefix ID resolution

Web: absorb button on fluid entities, 'a' keyboard shortcut,
source picker modal

web/app.js

@@ -85,6 +85,14 @@
       });
       return resp.json();
     },
+    async absorbEntity(targetId, sourceId) {
+      const resp = await fetch('/api/entities/' + targetId + '/absorb', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ source_id: sourceId }),
+      });
+      return resp.json();
+    },
     async listTags() {
       const resp = await fetch('/api/tags');
       return resp.json();
@@ -269,6 +277,7 @@
       actions += `<button class="action-btn" onclick="nibApp.demoteEntity('${e.id}')">demote</button>`;
     } else {
       actions += `<button class="action-btn primary" onclick="nibApp.showPromote('${e.id}')">promote</button>`;
+      actions += `<button class="action-btn" onclick="nibApp.showAbsorb('${e.id}')">absorb</button>`;
     }
     actions += `<button class="action-btn danger" onclick="nibApp.deleteEntity('${e.id}')">delete</button>`;
 
@@ -469,6 +478,44 @@
       }
     },
 
+    showAbsorb(targetId) {
+      const target = state.entities.find(x => x.id === targetId);
+      if (!target) return;
+      if (target.card_type) return;
+
+      const modal = $('#absorb-modal');
+      modal.dataset.targetId = targetId;
+      const list = $('#absorb-source-list');
+
+      const sources = state.entities.filter(x => x.id !== targetId);
+      if (!sources.length) { list.innerHTML = '<div class="detail-empty">no other entities</div>'; }
+      else {
+        list.innerHTML = sources.map(e => {
+          const g = displayGlyph(e);
+          const gc = glyphClass(e);
+          return `<div class="absorb-source-item" data-id="${e.id}">
+            <span class="entity-glyph ${gc}">${g}</span>
+            <span class="entity-body">${escHtml(e.body)}</span>
+          </div>`;
+        }).join('');
+      }
+
+      list.querySelectorAll('.absorb-source-item').forEach(el => {
+        el.addEventListener('click', async () => {
+          modal.classList.add('hidden');
+          modal.classList.remove('visible');
+          await api.absorbEntity(targetId, el.dataset.id);
+          await loadEntities();
+          await loadTags();
+          const idx = state.entities.findIndex(x => x.id === targetId);
+          if (idx >= 0) selectEntity(idx);
+        });
+      });
+
+      modal.classList.remove('hidden');
+      modal.classList.add('visible');
+    },
+
     async toggleStep(id, stepIdx) {
       const e = state.entities.find(x => x.id === id);
       if (!e || !e.card_data) return;
@@ -520,13 +567,14 @@
     });
   });
 
-  $('.modal-backdrop').addEventListener('click', closeModal);
-  $('.modal-close').addEventListener('click', closeModal);
+  $$('.modal-backdrop').forEach(el => el.addEventListener('click', closeModal));
+  $$('.modal-close').forEach(el => el.addEventListener('click', closeModal));
 
   function closeModal() {
-    const modal = $('#promote-modal');
-    modal.classList.add('hidden');
-    modal.classList.remove('visible');
+    $$('.modal.visible').forEach(m => {
+      m.classList.add('hidden');
+      m.classList.remove('visible');
+    });
   }
 
   // ========== Keyboard shortcuts ==========
@@ -541,7 +589,8 @@
       return;
     }
 
-    if ($('#promote-modal').classList.contains('visible')) {
+    if ($('#promote-modal').classList.contains('visible') ||
+        $('#absorb-modal').classList.contains('visible')) {
       if (ev.key === 'Escape') closeModal();
       return;
     }
@@ -586,6 +635,11 @@
         startEditBody();
         break;
       }
+      case 'a': {
+        const e = state.entities[state.selectedIndex];
+        if (e && !e.card_type) nibApp.showAbsorb(e.id);
+        break;
+      }
       case '1': switchView('stream'); break;
       case '2': switchView('cards'); break;
     }