fix(models): coerce Contact.birthday + relax Table.owner_display_name

Two upstream Pydantic ValidationErrors that took down whole list responses.

#704: Contact.birthday is declared str, but vobject parses BDAY as a
datetime.date — any contact with a populated BDAY broke nc_contacts_list_contacts
entirely. Add a field_validator(mode="before") that coerces date / datetime
to ISO strings. Strings and None pass through unchanged. Defense in depth:
existing call sites already coerce, but the model is now correct on its own
so any future code path that constructs Contact from raw vobject output
stays safe.

#728: Tables app v2.0.1 stopped emitting owner_display_name on the top-level
table payload (still present inside views via get_schema), so list_tables
failed for every user with a Pydantic ValidationError. Make the field
Optional[str] = None — captures the value when present, won't blow up when
missing.

Six new direct-construction unit tests in tests/unit/test_response_models.py
pin both fixes (date / datetime / str / None for birthday; with / without
owner_display_name for Table) so the regressions can't recur silently.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/models/contacts.py

@@ -1,8 +1,9 @@
 """Pydantic models for Contacts app responses."""
 
+from datetime import date, datetime
 from typing import Any, Dict, List, Optional
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_validator
 
 from .base import BaseResponse, StatusResponse
 
@@ -57,6 +58,21 @@ class Contact(BaseModel):
     )
     etag: Optional[str] = Field(None, description="ETag for versioning")
 
+    @field_validator("birthday", mode="before")
+    @classmethod
+    def _coerce_birthday(cls, value: Any) -> Any:
+        """Accept ``date``/``datetime`` from vobject and serialise to ISO string.
+
+        vobject parses BDAY into ``datetime.date`` (or ``datetime.datetime``);
+        the Pydantic model stores it as ``str``. Without this coercion any
+        contact with a populated BDAY blew up the entire ``list_contacts``
+        response (#704, #672). Strings and ``None`` pass through unchanged so
+        callers can still construct contacts with raw ISO input.
+        """
+        if isinstance(value, (date, datetime)):
+            return value.isoformat()
+        return value
+
     @property
     def primary_email(self) -> Optional[str]:
         """Get the primary email address."""

nextcloud_mcp_server/models/tables.py

@@ -72,7 +72,12 @@ class Table(BaseModel):
     title: str = Field(description="Table title")
     emoji: Optional[str] = Field(None, description="Table emoji")
     ownership: str = Field(description="Table ownership")
-    owner_display_name: str = Field(description="Display name of table owner")
+    # Tables app v2.0.1 stopped emitting owner_display_name at the top level
+    # (still present inside views via get_schema). Optional avoids a 100% failure
+    # rate on list_tables — see #728.
+    owner_display_name: Optional[str] = Field(
+        None, description="Display name of table owner"
+    )
     created_by: Optional[str] = Field(None, description="User who created the table")
     created_at: Optional[str] = Field(None, description="Table creation timestamp")
     last_edit_by: Optional[str] = Field(