Uncertainty engine: orphan sweep cron

[ssilvius]

Phase 1 of the uncertainty engine spike. See docs/designs/uncertainty-engine.md.

Scope:

• Hourly cron handler on the Worker
• UPDATE uncertainty_prediction SET state = 'orphaned' WHERE state = 'emitted' AND orphan_after < unixepoch() * 1000
• Bounded query, exit cleanly
• Wire into wrangler.jsonc triggers

Dependency: routes issue (table exists, schema is real).

Tests: unit test the SQL builder against an in-memory state.