style: apply ruff's automatic fixes and formatter

Mechanical only, and separated from the judgment calls that follow so the
reviewable changes are not buried in a 98-file whitespace diff.

227 automatic fixes: 60 blank lines carrying whitespace, 60 unsorted import
blocks, 34 Optional[X] to X | None, 28 unused imports, 16 deprecated typing
imports, 12 datetime.timezone.utc to datetime.UTC, and assorted smaller
modernisations. Then `ruff format` over src and tests: 98 files reformatted,
35 already conforming.

No file among the unused-import findings defines __all__ or is an __init__.py,
so nothing here removes a re-export.

`make test`: 658 passed, unchanged from HEAD.

Two things observed while verifying, neither addressed here:

`pytest tests/` cannot collect — tests/e2e/test_orchestration_e2e.py uses an
`e2e` marker that is not registered, and the config is strict about markers.
This fails identically at HEAD, so it predates this change; `make test` passes
because it ignores tests/e2e, tests/integration and tests/contracts.

test_tatlock_tool_call_logging_calculator is flaky. It failed once in a full run
with these changes and passed on the next, passes in isolation with them, and
fails in isolation at HEAD. It is order- or timing-dependent, not a regression
from this commit — established by running the full suite both ways rather than
by reasoning about which change could have caused it.

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

src/core/memory_service.py

@@ -21,14 +21,14 @@ Usage:
     # Get session context
     ctx = await memory_service.get_session_context(conversation_id)
 """
-from datetime import datetime, timezone
+
+from datetime import UTC, datetime
 from enum import Enum
 from typing import Any
 
 from pydantic import BaseModel, Field
 
-from .config import config
-from .context import get_user, get_conversation_id
+from .context import get_conversation_id, get_user
 from .embeddings import get_embedding_client
 from .logging_config import get_logger
 from .memory_cache import get_memory_cache
@@ -40,22 +40,24 @@ logger = get_logger(__name__)
 
 class MemoryType(str, Enum):
     """Types of memories stored in Qdrant."""
-    USER_PROFILE = "user_profile"      # Name, location, timezone
-    PREFERENCE = "preference"          # Units, language, theme
-    LEARNED_FACT = "learned_fact"      # "My car is a Tesla"
+
+    USER_PROFILE = "user_profile"  # Name, location, timezone
+    PREFERENCE = "preference"  # Units, language, theme
+    LEARNED_FACT = "learned_fact"  # "My car is a Tesla"
 
 
 class MemoryRecord(BaseModel):
     """A memory record stored in Qdrant."""
+
     id: str
     type: MemoryType
-    key: str                           # e.g., "location", "timezone", "car"
-    value: str                         # The actual content
+    key: str  # e.g., "location", "timezone", "car"
+    value: str  # The actual content
     keywords: list[str] = Field(default_factory=list)
-    importance: float = 0.5            # 0.0 - 1.0
-    source: str = "explicit"           # "explicit" | "inferred" | "conversation"
-    created_at: str = Field(default_factory=lambda: datetime.now(timezone.utc).isoformat())
-    updated_at: str = Field(default_factory=lambda: datetime.now(timezone.utc).isoformat())
+    importance: float = 0.5  # 0.0 - 1.0
+    source: str = "explicit"  # "explicit" | "inferred" | "conversation"
+    created_at: str = Field(default_factory=lambda: datetime.now(UTC).isoformat())
+    updated_at: str = Field(default_factory=lambda: datetime.now(UTC).isoformat())
 
 
 class MemoryService:
@@ -528,7 +530,7 @@ class MemoryService:
                 "keywords": keywords,
                 "importance": importance,
                 "source": source,
-                "updated_at": datetime.now(timezone.utc).isoformat(),
+                "updated_at": datetime.now(UTC).isoformat(),
             }
 
             result = await self.qdrant.upsert_memory(