tiemzone udpate on all pages that requrie timezone updating

docs/00-SYSTEM/TIMEZONE.md

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+# Timezone Standard
+
+## Purpose
+This document defines the single-source timezone standard for IGNY8 and how all future time-related features must use it.
+
+## Single Source of Truth
+- **Account timezone** is the canonical timezone for all user-visible times and scheduling UI.
+- The value is stored on the Account model as `account_timezone` (IANA name, e.g., `America/New_York`).
+- Selection modes:
+  - **Country-derived**: timezone is derived from billing country.
+  - **Manual**: user picks an IANA timezone that maps to a UTC offset list.
+
+## Storage Rules
+- **Persist timestamps in UTC** in the database.
+- **Never store local times** without timezone context.
+- Store user selection in `Account.account_timezone` and (when needed) `timezone_mode` and `timezone_offset` for UI display.
+
+## Display Rules (Frontend)
+- All UI formatting must use the account timezone.
+- Use shared helpers:
+  - `getAccountTimezone()` for the active timezone.
+  - `formatDate()`, `formatDateTime()`, `formatRelativeDate()` for consistent formatting.
+- **Do not** call `toLocaleDateString()` or `toLocaleTimeString()` without passing the account timezone.
+
+## Scheduling Rules
+- All scheduling inputs in UI are **account timezone**.
+- Convert to UTC before sending to the backend.
+- All API payloads for scheduling must send ISO-8601 with timezone offset.
+- The backend stores scheduled datetimes in UTC.
+
+## Backend API Contract
+- Endpoints that return timestamps should return UTC ISO strings.
+- Endpoints that return “server time” should return **account-local time** for display, plus the account timezone identifier.
+- If the account timezone is invalid or missing, fall back to `UTC`.
+
+## Country List Source
+- Country list must be fetched from `/v1/auth/countries/`.
+- No hardcoded country lists in UI or backend responses.
+
+## Implementation Checklist (New Features)
+1. **Input**: confirm user inputs are in account timezone.
+2. **Conversion**: convert to UTC before persistence or scheduling.
+3. **Storage**: store in UTC only.
+4. **Output**: format all timestamps with account timezone helpers.
+5. **API**: ensure responses include timezone-aware context when needed.
+
+## Guardrails
+- Never introduce a second timezone source per user/site.
+- Do not mix server timezone with account timezone in UI.
+- Avoid timezone math in the UI; prefer helpers and backend-provided values when possible.
+
+## Examples
+- **Display date in UI**:
+  - Use `formatDateTime(timestamp)` to render in account timezone.
+- **Schedule content**:
+  - User selects date/time in account timezone → convert to ISO → send to `/schedule/`.
+
+## Troubleshooting
+- If times appear “off”:
+  - Check account timezone is set.
+  - Confirm UI uses helpers.
+  - Confirm backend converts to UTC before save.
+
+---
+Owner: Platform
+Last updated: 2026-01-19