fix(core): update services to match issue #8 requirements

- Set created_at timestamp at service layer using time.time()
- Add PermissionError when non-creator tries to edit/delete
- Add ValueError when tracking non-existent bounty
- Rename create_bounty to add_bounty (matches spec)
- Add clear_link and clear_due parameters for partial updates
- Track timestamps for tracked bounties too

core/services.py

@@ -4,6 +4,9 @@ These services orchestrate operations through storage ports.
 No implementation details - pure orchestration layer.
 """
 
+import time
+from typing import Optional
+
 from core.models import Bounty, RoomData, TrackingData, TrackedBounty
 from core.ports import RoomStorage, TrackingStorage
 
@@ -12,20 +15,26 @@ class RoomBountyService:
     """Service for managing bounties within a room.
 
     Orchestrates bounty operations through a RoomStorage port.
+
+    A room is identified by room_id:
+    - Negative room_id: Telegram group
+    - Positive room_id: DM/personal context
+
+    This single service handles both group and personal bounties.
     """
 
     def __init__(self, storage: RoomStorage):
         self._storage = storage
 
-    def create_bounty(
+    def add_bounty(
         self,
         room_id: int,
-        text: str | None,
-        link: str | None,
-        due_date_ts: int | None,
-        created_by_user_id: int,
+        user_id: int,
+        text: Optional[str] = None,
+        link: Optional[str] = None,
+        due_date_ts: Optional[int] = None,
     ) -> Bounty:
-        """Create a new bounty in a room. Returns the created bounty."""
+        """Add a new bounty to a room. Returns the created bounty."""
         room_data = self._storage.load(room_id)
         if room_data is None:
             room_data = RoomData(room_id=room_id, bounties=[], next_id=1)
@@ -35,8 +44,8 @@ class RoomBountyService:
             text=text,
             link=link,
             due_date_ts=due_date_ts,
-            created_at=0,
-            created_by_user_id=created_by_user_id,
+            created_at=int(time.time()),
+            created_by_user_id=user_id,
         )
 
         room_data.bounties.append(bounty)
@@ -60,20 +69,28 @@ class RoomBountyService:
         self,
         room_id: int,
         bounty_id: int,
-        text: str | None = None,
-        link: str | None = None,
-        due_date_ts: int | None = None,
+        user_id: int,
+        text: Optional[str] = None,
+        link: Optional[str] = None,
+        due_date_ts: Optional[int] = None,
+        clear_link: bool = False,
+        clear_due: bool = False,
     ) -> bool:
-        """Update a bounty. Returns False if not found."""
+        """Update a bounty. Only creator can update. Raises PermissionError if not creator."""
         bounty = self._storage.get_bounty(room_id, bounty_id)
         if bounty is None:
             return False
 
+        if bounty.created_by_user_id != user_id:
+            raise PermissionError("Only the creator can edit this bounty.")
+
         updated = Bounty(
             id=bounty.id,
             text=text if text is not None else bounty.text,
-            link=link if link is not None else bounty.link,
-            due_date_ts=due_date_ts if due_date_ts is not None else bounty.due_date_ts,
+            link=None if clear_link else (link if link is not None else bounty.link),
+            due_date_ts=None
+            if clear_due
+            else (due_date_ts if due_date_ts is not None else bounty.due_date_ts),
             created_at=bounty.created_at,
             created_by_user_id=bounty.created_by_user_id,
         )
@@ -81,12 +98,15 @@ class RoomBountyService:
         self._storage.update_bounty(room_id, updated)
         return True
 
-    def delete_bounty(self, room_id: int, bounty_id: int) -> bool:
-        """Delete a bounty. Returns False if not found."""
+    def delete_bounty(self, room_id: int, bounty_id: int, user_id: int) -> bool:
+        """Delete a bounty. Only creator can delete. Raises PermissionError if not creator."""
         bounty = self._storage.get_bounty(room_id, bounty_id)
         if bounty is None:
             return False
 
+        if bounty.created_by_user_id != user_id:
+            raise PermissionError("Only the creator can delete this bounty.")
+
         self._storage.delete_bounty(room_id, bounty_id)
         return True
 
@@ -97,11 +117,16 @@ class TrackingService:
     Orchestrates tracking operations through a TrackingStorage port.
     """
 
-    def __init__(self, storage: TrackingStorage):
+    def __init__(self, storage: TrackingStorage, room_storage: RoomStorage):
         self._storage = storage
+        self._room_storage = room_storage
 
     def track_bounty(self, room_id: int, user_id: int, bounty_id: int) -> bool:
-        """Start tracking a bounty. Returns False if already tracking."""
+        """Start tracking a bounty. Verifies bounty exists first. Raises ValueError if not found."""
+        bounty = self._room_storage.get_bounty(room_id, bounty_id)
+        if bounty is None:
+            raise ValueError("Bounty not found.")
+
         tracking_data = self._storage.load(room_id, user_id)
         if tracking_data is None:
             tracking_data = TrackingData(room_id=room_id, user_id=user_id, tracked=[])
@@ -110,12 +135,12 @@ class TrackingService:
             if tracked.bounty_id == bounty_id:
                 return False
 
-        tracked = TrackedBounty(bounty_id=bounty_id, created_at=0)
+        tracked = TrackedBounty(bounty_id=bounty_id, created_at=int(time.time()))
         self._storage.track_bounty(room_id, user_id, tracked)
         return True
 
     def untrack_bounty(self, room_id: int, user_id: int, bounty_id: int) -> bool:
-        """Stop tracking a bounty. Returns False if not tracking."""
+        """Stop tracking a bounty. Returns True if was tracking, False if not found."""
         tracking_data = self._storage.load(room_id, user_id)
         if tracking_data is None:
             return False