fix: keep the belt worker page within its budget

[ZeroPoint95]

• Shorten the belt worker page while preserving its declaration, completion, ownership, cleanup and editing rules. Its composed prompt exceeded the existing sixteen-KiB bound after the latest declaration guidance.
• Run the unchanged composed-page test in the CI light gate and local quick/PR gate, including embedded Markdown changes that do not select a touched Go package.

Validation:

• Rendered prompt: 15,710 bytes, 674 bytes below the unchanged strict 16,384-byte limit. The new target rejects the original page at 16,640 bytes.
• make build, nine existing focused regressions, and exact-base make pr-ready passed. Independent review covers the final source and gate wiring.