Add neuron-dev-setup: one-command CORE dev stack onboarding installer

Scaffolds a reproducible, idempotent installer that stands up the four native
launchd core services (soul :7770, engram :8742, mcp-wrapper :17779,
mcp-proxy :7779), seeds a fresh engram with the genesis identity via forge, and
installs the Claude Code config (neuron agent + core hooks + local MCP). Fully
templated to the invoking user's $HOME; Anthropic key prompted and stored in
Keychain; no secrets committed. Personal automations and synapse-dependent hooks
excluded from core.

neuron-dev-setup/templates/claude/mcp.json.tmpl

@@ -0,0 +1,8 @@
+{
+  "mcpServers": {
+    "neuron": {
+      "type": "http",
+      "url": "http://127.0.0.1:@@PROXY_PORT@@/"
+    }
+  }
+}