Fix: limit widget data cache keys to declared query values

[SandObserver]

Summary

• Build the /api/widget-data cache key and ctx.params from endpoint plus the names the widget manifest lists in a new params field. Other query values are dropped.
• Validate params in the manifest: at most 8 query parameter names, no duplicates, endpoint not listed.
• Cap cached replies per widget at 16 in latest(), dropping the oldest settled entries and never a refresh in flight.
• Declare seed in the System Summary manifest.

Testing
All green. Added tests for the parameter filter, manifest validation, the per-widget cap, junk query values sharing one refresh, and a guard that every value a data.js reads is declared.

Changelog

Added

• Let a widget manifest list the query parameters its data function reads.

Fixed

• Stop extra query values on widget data requests from filling server memory and multiplying upstream calls.

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.