Handle consolidation errors raised during manager creation

[cyc60]

Description

In process() only get_target_source() was wrapped in try/except ConsolidationError; the ConsolidationManager.create(...) call above it was not. A ConsolidationError raised during manager creation (e.g. Cannot determine balance for source validator index ... in pending consolidation) escaped to the generic exception handler in consolidate(), producing a verbose log line and bare exit code 1 instead of the clean Error: ... message every other validation error in this flow produces.

The try block now covers manager creation as well, so all ConsolidationErrors surface as a clean ClickException.

Note: src/validators/commands/tests/test_consolidate.py is also created by #801; whichever merges second will need a trivial test-file merge.