refactor(time): migrate runtime time handling to Temporal

docs/specs/HOUSEBOT-074-temporal-migration.md

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+# HOUSEBOT-074 Temporal Migration
+
+## Goal
+
+Move runtime time handling from ad-hoc `Date` usage to `Temporal` via `@js-temporal/polyfill`.
+
+## Why
+
+- Bun does not provide native `Temporal` yet, so the polyfill is the safe path.
+- The bot has already had production failures caused by `Date` values crossing Bun/Postgres boundaries inconsistently.
+- Time handling should be explicit and deterministic at adapter boundaries.
+
+## Slice 1
+
+- Add shared Temporal helpers in `@household/domain`
+- Migrate anonymous feedback service and repository
+- Migrate Telegram pending-action expiry handling
+- Migrate mini app auth timestamp verification
+
+## Boundary Rules
+
+- Business/application code uses `Temporal.Instant` instead of `Date`
+- Database adapters convert `Temporal.Instant` to SQL-compatible values on write
+- Database adapters normalize string/`Date` timestamp values back to `Temporal.Instant` on read
+- Telegram epoch timestamps remain numeric seconds at the API edge
+
+## Non-goals
+
+- Full repo-wide `Date` removal in one change
+- Database schema changes
+- Billing-period model replacement
+
+## Follow-up Slices
+
+- Finance command service and finance repository date handling
+- Purchase ingestion timestamps
+- Reminder job scheduling timestamps
+- Test helpers that still construct `Date` values for untouched paths
+
+## Acceptance
+
+- No raw `Date` values cross the anonymous-feedback, pending-action, or mini app auth application boundaries
+- `bun run typecheck`
+- `bun run test`
+- `bun run build`