fx v0.0.15 cuts memory, boosts speed

This is a quietly important performance release: for terminal agents, lower memory pressure and faster recovery matter more than flashy surface features.

• –A synthetic benchmark with 96 MiB of saved images measured 69.5% lower peak memory and 3.3× faster turn completion versus v0.0.14.
• –Model-catalog refreshes without restarting reduce friction when switching models or providers.
• –`/fork` makes experimentation safer by letting developers branch from earlier prompts instead of disrupting a working session.
• –WebAssembly completed 140 image-heavy turns where the previous implementation ran out of memory at turn 102.
• –The release strengthens fx’s positioning as a lightweight, embeddable alternative to heavier coding-agent environments.