Initialize GovOPlaN calendar module

AGENTS.md

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+# GovOPlaN Calendar Codex Guide
+
+## Scope
+
+This repository owns the `calendar` module: calendar collections, VEVENT storage, iCalendar import/export, availability primitives, backend module manifest, and `@govoplan/calendar-webui`.
+
+Core owns auth, tenants, RBAC, database/session primitives, shared WebUI shell/components, and module discovery. Calendar integrations with tasks, mail, scheduling, appointments, workflow, DMS, notifications, and external groupware must stay optional and use core module metadata or capability boundaries.
+
+## Local Commands
+
+Install and run through core:
+
+```bash
+cd /mnt/DATA/git/govoplan-core
+./.venv/bin/python -m pip install -r requirements-dev.txt
+```
+
+Run focused calendar tests from the core environment:
+
+```bash
+cd /mnt/DATA/git/govoplan-core
+PYTHONPATH=/mnt/DATA/git/govoplan-calendar/src:/mnt/DATA/git/govoplan-tenancy/src:/mnt/DATA/git/govoplan-access/src:/mnt/DATA/git/govoplan-core/src ./.venv/bin/python -m unittest discover -s /mnt/DATA/git/govoplan-calendar/tests
+```
+
+## Working Rules
+
+- Keep calendar semantics in this module, not core.
+- Preserve unknown iCalendar properties and parameters unless a migration explicitly changes the storage model.
+- Do not import optional modules directly from calendar. Use capabilities or API contracts for tasks, mail, scheduling, appointments, and external groupware.
+- Treat recurrence expansion, free/busy, and CalDAV sync as calendar-owned primitives even when another module initiates them.