feat(circles): create_circle + add_member_to_circle (v0.7.0)

- acccreatefamily endpoint creates a new circle (returns numeric ID)
- accinvite endpoint invites new users by email (familyId, identifier, role, firstname)
- fw_client now detects a00.ex errors (was only checking a00.un before)
- New modules/circles.py with FamilyRoleTypeEnum constants
- SPEC.md updated with acccreatefamily, accinvite, accupdatefamily docs
- Note: circle deletion not supported by FW API (metadelete → "delete not supported")
- Note: accinvite only works for new (non-existing) FW accounts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/mcp_familywall/modules/circles.py

@@ -0,0 +1,10 @@
+"""Circle (family group) helpers for the Family Wall MCP server."""
+
+from __future__ import annotations
+
+# Valid family role types known to the Family Wall API (FamilyRoleTypeEnum).
+# Only "Unknown" has been verified to be accepted by accinvite.
+ROLE_UNKNOWN = "Unknown"
+
+# Default role used when inviting new members.
+DEFAULT_INVITE_ROLE = ROLE_UNKNOWN