Add Zapier interface simulator, tree-node Merkle lookups, and user docs

In-process trace console validates hops, faults, recoveries, and
suggested changes before zapier-platform push. User guide covers
signup through central-chain and bulk-summary tree-node hash lookup.

docs/02-architecture/tree-nodes.md

@@ -0,0 +1,44 @@
+# Tree nodes: bulk Merkle summaries vs itemized chain seals
+
+The main Verae chain stores **hash + time + block + certificate**. A Zap that timestamps one document writes that document’s SHA-256 as its own seal.
+
+A **batch** of many documents is different: middleware builds a Merkle tree of the item hashes, seals **only the Merkle root** on the chain, and writes each **leaf proof** to external tree-node NATS archives. A later lookup of a member hash will **miss** on the central chain unless the Zap also queries tree nodes.
+
+```text
+Zapier  HTTPS  zappier-edge  HTTPS  middleware
+                                      |
+                         Merkle root  |  verae.archive.put kind=tree
+                         (chain seal) |  (leaf proof, sharded)
+                                      v
+                               tree-node-east/west/central
+                               bloom miss = silence
+                                      ^
+              hash lookup includeTree |  verae.archive.query
+                                      |  kinds=["tree"]
+                              aggregator merges proof + root seal
+```
+
+## When to use which Zapier search
+
+| Search | Hits |
+|--------|------|
+| Find Timestamp by SHA256 | Hash was registered as its own chain seal |
+| Find Hash (tree nodes + central chain) | Chain first, then `includeTree=true` broadcast |
+
+## Receipt shape for a bulk leaf
+
+```json
+{
+  "sha256": "<leaf>",
+  "exists": true,
+  "itemizedOnMainChain": false,
+  "merkleRoot": "<root sealed on chain>",
+  "proofOk": true,
+  "receipts": [
+    { "kind": "seal", "of": "merkleRoot", "sha256": "<root>", "certificate": "…" },
+    { "kind": "tree-leaf", "archiveId": "tree-node-east", "proof": […], "leafIndex": 1 }
+  ]
+}
+```
+
+Validate this path in the simulator (`packages/verae-zapier-simulator`) before pushing the Zapier app.