chore(release): clean up repo for v0.0.1 release

Excluded from release bundle:
- CONTEXT.md, CHANGELOG.md (agent/project working notes)
- client-app/ (React Native messenger — tracked separately)
- contracts/hello_go/ (unused standalone example)

Kept contracts/counter/ and contracts/name_registry/ as vm-test fixtures
(referenced by vm/vm_test.go; NOT production contracts).

Docs refactor:
- docs/README.md — new top-level index with cross-references
- docs/quickstart.md — rewrite around single-node as primary path
- docs/node/README.md — full rewrite, all CLI flags, schema table
- docs/api/README.md — add /api/well-known-version, /api/update-check
- docs/contracts/README.md — split native (Go) vs WASM (user-deployable)
- docs/update-system.md — new, full 5-layer update system design
- README.md — link into docs/, drop CHANGELOG/client-app references

Build-time version system (inherited from earlier commits this branch):
- node --version / client --version with ldflags-injected metadata
- /api/well-known-version with {build, protocol_version, features[]}
- Peer-version gossip on dchain/version/v1
- /api/update-check against Gitea release API
- deploy/single/update.sh with semver guard + 15-min systemd jitter

client-app/app.json

@@ -1,36 +0,0 @@
-{
-  "expo": {
-    "name": "DChain Messenger",
-    "slug": "dchain-messenger",
-    "version": "1.0.0",
-    "orientation": "portrait",
-    "userInterfaceStyle": "dark",
-    "backgroundColor": "#0d1117",
-    "ios": {
-      "supportsTablet": false,
-      "bundleIdentifier": "com.dchain.messenger"
-    },
-    "android": {
-      "package": "com.dchain.messenger",
-      "softwareKeyboardLayoutMode": "pan"
-    },
-    "web": {
-      "bundler": "metro",
-      "output": "static"
-    },
-    "plugins": [
-      "expo-router",
-      "expo-secure-store",
-      [
-        "expo-camera",
-        {
-          "cameraPermission": "Allow DChain to scan QR codes for node configuration."
-        }
-      ]
-    ],
-    "experiments": {
-      "typedRoutes": false
-    },
-    "scheme": "dchain"
-  }
-}