Epic: Performance at scale

[ApocDev]

Keep startup and editing responsive as projects and production blocks grow. This is the product-runtime follow-up to the completed SQLite and solve-path audit in #138.

Sub-issues:

• Reduce large recipe-grid render cost #154 — reduce large-block rendering cost.
• Split the oversized client entry chunk #139 — split the oversized client entry chunk.

Use measured wall-clock and browser behavior as the governing signals. For large blocks, take the profiled lower-risk path before attempting variable-height row virtualization.