Fix: MoE Memory Budgeting and Dynamic Multimodal Tokens

[roydsouza]

Description

This PR addresses two critical issues identified during an adversarial audit of SwiftLM on Apple Silicon (M5):

1. MoE-Aware Memory Budgeting: Previously, MoE expert weights were not accounted for in the physical RAM budget when using SSD streaming. This led to 'swap-storms' as active experts were paged in over the limit. This PR adds a 2GB safety buffer for MoE models and includes a high-swap usage monitor.
2. Dynamic Multimodal Token Resolution: Resolved hardcoded boaToken (255010) and eoaToken (255011) by extracting them dynamically from config.json. This fixes expert routing for non-Qwen multimodal models.

Changes

• Added moeBuffer to computeSSDMemoryBudget.
• Integrated sysctl vm.swapusage check in Server.swift.
• Implemented extractMultimodalTokens in OmniModelFactory to resolve BOA/EOA tokens from config.

Verified on Apple Silicon M5 with Gemma 4 MoE.