fix(kanban): include default profile in on-disk assignees

[Interstellar-code]

Summary

• treat the implicit default profile as on-disk in Kanban assignee/profile enumeration
• keep named-profile discovery under <default-root>/profiles/<name>/config.yaml
• add regression coverage for standard and custom HERMES_HOME roots

Problem

Kanban's list_profiles_on_disk() only recognized named profiles stored under profiles/<name>/config.yaml. The implicit default profile lives at the Hermes root itself (~/.hermes or custom HERMES_HOME) and therefore showed up as on_disk: false in consumers like the dashboard / SwitchUI profiles list even though it is a real usable profile.

Fix

When the default Hermes root exists, include default in the discovered on-disk profile set. Keep existing named-profile enumeration unchanged.

Test Plan

• ~/.hermes/hermes-agent/venv/bin/python -m pytest tests/hermes_cli/test_kanban_core_functionality.py -q -n 4 -k 'list_profiles_on_disk or known_assignees or pid_alive or detect_crashed_workers'

[alt-glitch]

Related to #19020, #19017 — extends the HERMES_HOME-aware profile discovery to also include the implicit default profile.

[teknium1]

Merged via PR #20170 (commit 542e06c). Your commit was cherry-picked onto current main with your authorship preserved in git log. Thanks — clean fix with good test coverage for both the standard and custom HERMES_HOME cases.

#20170