Dev-only bulk delete all campaigns; deleteCollection SQL bulk + gates

Feature: debug button to wipe all campaigns/encounters/logs in dev builds.
Previously bulk delete fetched all logs per campaign, client-filtered,
batchWrite — 30s+/campaign. Now SQL bulk DELETE, no fetch.

Server (server/db.js, server/index.js):
- deleteCollection(collPath, {where}) — SQL DELETE FROM docs WHERE parent=?,
  optional where-filter. Broadcasts deletions to WS subscribers.
- DELETE /api/collection endpoint
- Gate: ALLOW_DEV_ENDPOINTS=1 env OR createServer({allowDevEndpoints:true})
- createServer accepts allowDevEndpoints param (tests bypass env)

Storage (src/storage/server.js, src/storage/firebase.js):
- deleteCollection(path, whereField, whereValue) both adapters
- Firebase: fetch matching + batch-delete (firestore no bulk), 500-chunk
- Gate: throws if NODE_ENV not development/test
- Contract-tested both backends

App (src/App.js):
- deleteCampaignCascade refactored (reusable, no try/catch split)
- handleDeleteAllCampaigns: Promise.all per campaign, deleteCollection for
  encounters (no fetch), deleteCollection logs once globally, parallel
- Button dev-gated (NODE_ENV), confirm modal, hidden when no campaigns

Mock fixes (surfaced by new tests):
- firebase firestore mock: added where() export, getDocs applies constraints
  (was returning all docs ignoring query constraints — pre-existing gap)

Tests:
- contract: deleteCollection (bulk, where-filter, empty) both backends
- server-contract: live deleteCollection (bulk, where, 403 gate)
- runStorageContract via makeStorage({allowDevEndpoints:true})

Safety (3 layers):
- UI button hidden in prod (NODE_ENV gate)
- storage method throws in prod (NODE_ENV gate)
- HTTP endpoint 403 in prod (env/param gate)

src/storage/firebase.js

@@ -130,6 +130,27 @@ export function createFirebaseStorage() {
       await batch.commit();
     },
 
+    // Bulk delete collection (optionally where-filtered). Firestore has no
+    // single bulk-by-path op: fetch matching docs, batch-delete in chunks
+    // of 500 (firestore batch limit). DEV ONLY.
+    async deleteCollection(path, whereField, whereValue) {
+      if (process.env.NODE_ENV !== 'development' && process.env.NODE_ENV !== 'test') {
+        throw new Error('deleteCollection: dev only');
+      }
+      let q = collection(db, path);
+      if (whereField) q = query(q, where(whereField, '==', whereValue));
+      const snap = await getDocsReal(q);
+      const docs = snap.docs;
+      let count = 0;
+      for (let i = 0; i < docs.length; i += 500) {
+        const batch = writeBatch(db);
+        for (const d of docs.slice(i, i + 500)) batch.delete(d.ref);
+        await batch.commit();
+        count += Math.min(500, docs.length - i);
+      }
+      return count;
+    },
+
     // Transactional undo via batch (atomic in firestore). Apply updates +
     // flip undone flag in single commit.
     async undo({ logPath, undo, redo = false }) {