post-audit: close remaining plugin HUD and slash-command migration gaps

[JeremyDev87]

Summary

A follow-up audit found three remaining plugin-level gaps after the recent status bar and command-migration work.

These issues are now small and well-scoped, but they are real user-facing mismatches:

• the status bar can lose the actor badge even when HUD state knows the active agent
• mode entry can preserve stale workflow state from the previous mode
• the published plugin package still does not fully match the documented /codingbuddy:* slash-command migration model

Why this parent issue exists

The recent work significantly improved the project, but these gaps still sit on important runtime edges:

• Claude Code status bar correctness
• workflow-state reset behavior
• distributable package vs. docs/runtime command model consistency

Each child issue is independently implementable and includes reproduction notes, scope, and acceptance criteria.

Child issues

• fix(plugin): make the status bar actor badge fall back to hud_state.activeAgent #1333
• fix(plugin): clear stale workflow state when entering a new mode #1334
• fix(plugin): finish the namespaced slash-command migration in the distributable package #1335

Recommended order

1. Fix HUD actor badge fallback from hud_state.activeAgent
2. Fix stale workflow-state leakage on mode entry
3. Close the namespaced slash-command migration gap in the distributable package

Validation target

When this parent issue is complete:

• the two-line status bar shows the correct actor more reliably
• switching modes no longer carries stale workflow state forward
• the plugin tarball and documentation describe the same slash-command model

[JeremyDev87]

All sub-issues merged: #1333 (PR #1339), #1334 (PR #1337), #1335 (PR #1338)