Polish: clearer errors, corrected docstrings, setuptools pin

- insert/upsert into a name that is actually a view now shows a
  clean error instead of a traceback
- db.view() on a name that is a table now says so in its error
- Database.__getitem__ docstring documents that views are returned
  for view names; hash_id docstring corrected (it is a column name,
  not a boolean)
- Registering two migrations with the same name in one set now
  raises ValueError at registration time instead of executing both
  and failing with IntegrityError at apply time
- build-system requires setuptools>=77, needed for the PEP 639
  license expression

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UnLnhsH25Nnv7LHhekUfPd

tests/test_migrations.py

@@ -198,3 +198,19 @@ def test_pending_and_applied_are_read_only(migrations):
     assert migrations.applied(db) == []
     # Neither call should have created the tracking table
     assert db.table_names() == []
+
+
+def test_duplicate_migration_name_errors():
+    migrations = Migrations("test")
+
+    @migrations()
+    def m001(db):
+        pass
+
+    with pytest.raises(ValueError) as ex:
+
+        @migrations(name="m001")
+        def m001_again(db):
+            pass
+
+    assert "m001" in str(ex.value)