chore: remove redundant sidecar/.help/ corpus (#63)

sidecar/.help/ was an early auto-scaffold from a stale-era
'attune-author init' inside sidecar/. It was never curated and
duplicates the root .help/ corpus entirely:

- Its 'attune-gui' feature (attune_gui/**) is a strict subset of
  root's 'sidecar' feature (sidecar/**).
- Its 'attune_gui-entry' feature points at the same file root's
  does (sidecar/attune_gui/app.py).
- Its 'attune-gui.egg-info' feature is a build artifact, not source.
- Its 'tests' feature is covered by root's broader sidecar/** glob.

The runtime never reads sidecar/.help/ — living_docs_store.py,
commands.py, and cowork_files.py all resolve .help/ via
project_root, which the federated config sets to the repo root.

Also drops the now-obsolete Makefile comment explaining why the
sidecar corpus was deferred — it no longer exists to defer.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: silversurfer562

Makefile

@@ -36,8 +36,6 @@ clean-editor:
 
 # Regenerate living-docs templates for the root .help/ corpus.
 # Calls Anthropic for polish — costs $$ on stale features.
-# Sidecar corpus (sidecar/.help/) is deferred and not maintained here;
-# see docs/specs/living-docs-regen-automation/ for the rationale.
 regen-templates:
 	uv run attune-author regenerate --help-dir .help