add rule date time

docs/standards/project-foundations.md

@@ -377,3 +377,17 @@ If ADR coverage is incomplete, this registry marks the gap explicitly.
 - ALLA OS Foundation Registry = COMPLETE
 - ALLA OS Reuse Discovery = READY
 - ALLA OS Governance Quality = IMPROVED
+
+## Date & Time Formatting Rules
+
+- All date and time rendering must use the shared formatter in `src/lib/date-format.ts`.
+- Never use `Date.prototype.toLocaleString()`, `toLocaleDateString()`, `toLocaleTimeString()`, or `Intl.DateTimeFormat()` directly inside React components.
+- UI date display standard:
+  - Date: `YYYY-MM-DD`
+  - DateTime: `YYYY-MM-DD HH:mm:ss`
+  - Time: `HH:mm:ss`
+- API responses must remain ISO-8601 UTC.
+- UI is responsible for formatting.
+- Timezone is fixed to `Asia/Bangkok`.
+- Calendar system must always use Gregorian (AD), never Buddhist Era (BE).
+- All formatting must be deterministic to ensure identical SSR and Client rendering and prevent React hydration mismatches.