Add URL-synced activity sorting controls

[silentgeckoaudit3801]

Summary

• add sort=newest|oldest support to the activity query contract and hook
• reflect activity filters, sort order, and page size in the /activity URL query string
• add Sort and Page size controls to the Activity page
• cover oldest-first ordering and invalid sort query parsing

Testing

• Not run locally; this workspace is intentionally avoiding project dependency/toolchain execution.