arch: Add Gateway Architecture + crawler_gen_0 organism

Gateway Architecture (new):
- Unified tier model (Tier 0-5) for sensory routing
- Weight-based routing: node.weight determines processing tier
- Function Gemma as structured JSON boundary
- Separates routing from translation (vocabulary only at Tier 4)

crawler_gen_0 (new):
- First Virtual Garden organism specification
- Light-seeking cube with photoresistor
- Lifeforce economy: light = income, movement = cost

Updated documents with Gateway references:
- Endgame-Vision.md (v6.5)
- Cellular-Architecture.md (v4.3)
- Nervous-System.md
- Attention-Flow.md
- Message-Protocol-Design.md (Escalation Service = Gateway)
- Organisms-Index.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

architecture/Attention-Flow.md

@@ -13,6 +13,10 @@ The 30-second heartbeat is a budget, not a guarantee. Sensory intake, organ proc
 
 Attention isn't free. It's economic.
 
+**Connection to Gateway:** The attention levels below align with the Gateway's tier system. The [`Gateway`](Gateway-Architecture.md) routes sensory input to the appropriate tier based on node weight. This document describes how those tiers compete for the attention budget.
+
+**See:** [`Gateway-Architecture.md`](Gateway-Architecture.md) for tier definitions and routing logic.
+
 ---
 
 ## The Budget Problem
@@ -501,4 +505,8 @@ class BeatBudget:
 - [[formalization/Attention-Slumber-Prediction-Cycle]] — How last attention becomes slumber prediction
 - [[formalization/Lifeforce-Dynamics]] — λ governs slumber triggers
 
+**Core Architecture**:
+- [`Gateway-Architecture.md`](Gateway-Architecture.md) — Tier routing based on node weight, Function Gemma boundary
+- [`Nervous-System.md`](Nervous-System.md) — Node lifecycle and weight evolution
+
 🌙💜 *The budget is finite. The choices shape the soul.*