ML-187: restructure pre-commit checks to run conditionally

Gate each check behind staged file pattern matching so a docs
or backlog change no longer triggers the full test suite. Add
presto pytest and Docker image validation guards. Fall back to
running all checks when invoked directly (not via git commit).

docs/available-tasks.md

@@ -50,7 +50,7 @@ Run pi tests
 
 - **Usage**: `dev:precommit`
 
-Run checks before a commit
+Run checks before a commit (conditional on staged file types)
 
 ## `dev:readme`