fix(VIOL-0064): raise on ambiguous agent-name folder match

[Muizzkolapo]

Summary

The agent-name resolver (FileHandler.get_agent_paths) walked the project tree and returned the first <name>/agent_config directory it happened to reach, silently. In a project where two directories share the same base name (multi-tenant / multi-workflow layouts), an operator running any CLI command with -a <name> could target the wrong workflow — reading and writing the wrong agent_io — with no warning or error.

Root cause: a first-match return inside os.walk.

Fix:

• Add FileHandler.find_all_specific_folders — collects every matching folder instead of returning the first.
• get_agent_paths now raises AmbiguousAgentName listing every candidate (full path + parent workflow directory) when two or more agent_config directories share the base name.
• 0-match and 1-match behavior is byte-identical ((None, None) and the single path, respectively).
• find_specific_folder (first-match) is left intact for the agent_io lookup and action-folder resolution — the agent_config raise fires first and covers the common case.

Why AmbiguousAgentName subclasses ValidationError: the sole caller (ProjectPathsFactory.get_agent_paths) re-raises ValidationError unchanged but wraps any other exception into a generic "Failed to get agent paths" message that would destroy the candidate list. Subclassing ValidationError lets the precise error — with its full candidate listing — propagate cleanly to every CLI command via create_project_paths, with no caller edit. This also aligns the ≥2-match case with the existing 0-match case, which already surfaces as a ValidationError.

Verification

• RED: the two ambiguous-fixture tests failed with DID NOT RAISE (proving the silent first-match bug), while single/zero/subclass baselines passed.
• GREEN: all five tests in tests/unit/utils/test_get_agent_paths_disambiguation.py pass after the fix, at both the util layer and the CLI-facing factory layer (candidate list survives, not re-wrapped).
• No regression: tests/unit/test_errors.py, tests/unit/utils/, tests/cli/test_cli_hardening.py (incl. the single-match test_project_root_reaches_file_handler), tests/workflow/test_runner.py, tests/unit/llm_invocation/test_agent_manager.py, tests/config/ — all pass.
• ruff check clean; ruff format --check clean.

Out of scope (follow-up)

agent_io ambiguity is not guarded — the agent_config raise fires first. Guard it the same way if a case arises. The separate AgentManager realtime resolver is a different code path and is untouched.