docs: add roadmap, ADRs, and initial HOUSEBOT specs

docs/specs/HOUSEBOT-004-reminders-and-scheduler.md

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+# HOUSEBOT-004: Reminders and Scheduler
+
+## Summary
+Schedule and deliver household billing reminders to dedicated Telegram topics.
+
+## Goals
+- Automate utility and rent reminders on configured dates.
+- Ensure idempotent sends and reliable retries.
+- Keep scheduling externalized via Cloud Scheduler.
+
+## Non-goals
+- Dynamic natural-language reminder editing.
+- Per-user DM reminders in v1.
+
+## Scope
+- In: scheduler endpoints, reminder generation, send guards.
+- Out: full statement rendering details.
+
+## Interfaces and Contracts
+- HTTP endpoints triggered by Cloud Scheduler:
+  - `/jobs/reminder/utilities`
+  - `/jobs/reminder/rent-warning`
+  - `/jobs/reminder/rent-due`
+- Job payload includes cycle and household references.
+
+## Domain Rules
+- Utilities reminder target: day 3 or 4 (configurable).
+- Rent warning target: day 17.
+- Rent due target: day 20.
+- Duplicate-send guard keyed by household + cycle + reminder type.
+
+## Data Model Changes
+- `reminder_dispatch_log`:
+  - `household_id`
+  - `billing_cycle`
+  - `reminder_type`
+  - `sent_at`
+  - `telegram_message_id`
+
+## Security and Privacy
+- Scheduler endpoints protected by shared secret/auth header.
+- No sensitive data in scheduler payloads.
+
+## Observability
+- Job execution logs with correlation IDs.
+- Success/failure counters per reminder type.
+- Alert on repeated send failures.
+
+## Edge Cases and Failure Modes
+- Telegram API temporary failure.
+- Scheduler retry causes duplicate call.
+- Missing household topic mapping.
+
+## Test Plan
+- Unit:
+  - date and reminder eligibility logic
+- Integration:
+  - endpoint auth and idempotency behavior
+- E2E:
+  - simulated month schedule through all reminder events
+
+## Acceptance Criteria
+- [ ] Scheduler endpoints implemented and authenticated.
+- [ ] Reminder sends are idempotent.
+- [ ] Logs and counters available for each job run.
+- [ ] Retry behavior validated.
+
+## Rollout Plan
+- Deploy with dry-run mode first, then enable live sends.