fix: cleanup codebase and sync SPEC with actual permissions

Phase 1: Ruff lint fixes
- Remove unused imports across all files
- Remove unused variables (now_utc, tz, ctx)
- Fix f-string without placeholders
- Fix E402 import order with noqa comments

Phase 2: Remove confusing hard delete from storage
- Removed delete_bounty() from RoomStorage Protocol (never used by app)
- Removed delete_bounty() from JsonFileRoomStorage (was hard delete)
- Removed corresponding tests (hard delete was never used)

Phase 3: Sync SPEC.md with actual code behavior
- Updated overview: admins can add/edit/delete (not 'anyone' + 'creator')
- Updated command table: /add, /edit, /delete are admin only
- Updated error handling messages

Test results: 96 passed (2 hard delete tests removed)

tests/test_ports.py

@@ -1,6 +1,5 @@
 """Tests for core/ports.py — storage interfaces."""
 
-import pytest
 
 from core.models import Bounty, RoomData, TrackingData, TrackedBounty
 from core.ports import RoomStorage, TrackingStorage
@@ -35,12 +34,6 @@ class SimpleRoomStorage:
                     self._rooms[room_id].bounties[i] = bounty
                     break
 
-    def delete_bounty(self, room_id: int, bounty_id: int) -> None:
-        if room_id in self._rooms:
-            self._rooms[room_id].bounties = [
-                b for b in self._rooms[room_id].bounties if b.id != bounty_id
-            ]
-
     def get_bounty(self, room_id: int, bounty_id: int) -> Bounty | None:
         if room_id in self._rooms:
             for b in self._rooms[room_id].bounties:
@@ -120,12 +113,6 @@ class MockRoomStorage:
                     self._rooms[room_id].bounties[i] = bounty
                     break
 
-    def delete_bounty(self, room_id: int, bounty_id: int) -> None:
-        if room_id in self._rooms:
-            self._rooms[room_id].bounties = [
-                b for b in self._rooms[room_id].bounties if b.id != bounty_id
-            ]
-
     def get_bounty(self, room_id: int, bounty_id: int) -> Bounty | None:
         if room_id in self._rooms:
             for b in self._rooms[room_id].bounties:
@@ -243,19 +230,6 @@ class TestRoomStorage:
         assert result is not None
         assert result.text == "Updated"
 
-    def test_delete_bounty(self):
-        storage = MockRoomStorage()
-        bounty = Bounty(
-            id=1,
-            text="Test",
-            link=None,
-            due_date_ts=None,
-            created_at=0,
-            created_by_user_id=123,
-        )
-        storage.add_bounty(-1001, bounty)
-        storage.delete_bounty(-1001, 1)
-        assert storage.get_bounty(-1001, 1) is None
 
 
 class TestTrackingStorage: