fix(kanban): include default profile in on-disk assignee enumeration (salvages #20123)

[teknium1]

The implicit default profile now shows up in Kanban's on-disk profile enumeration, so dashboard assignee pickers and known_assignees() no longer report it as on_disk: false.

Salvaged from #20123 (@Interstellar-code).

Root cause: list_profiles_on_disk() only enumerated directories under <root>/profiles/<name>/config.yaml. The default profile lives at the Hermes root itself (~/.hermes), not under a profiles/default/ subdirectory, so it fell through the filter even though it's a real runnable profile.

Changes

• hermes_cli/kanban_db.py: list_profiles_on_disk() now adds "default" to the result when the default Hermes root exists. Named-profile enumeration under <root>/profiles/<name>/config.yaml is unchanged.
• Tests updated for standard and custom HERMES_HOME roots.

Validation

	Before	After
Dashboard assignee list with default profile present	default: on_disk=False (confusing, hides a real option)	default: on_disk=True
test_kanban_core_functionality.py	-	119/119 pass
Broader kanban suite	-	335/335 pass (test_kanban_{db,cli,boards,core_functionality} + test_kanban_tools + test_kanban_dashboard_plugin)

Closes #20123

Co-authored-by: Interstellar-code 33978413+Interstellar-code@users.noreply.github.com