chore(drift-001): delete embedded echidnabot/ copy — standalone is canonical

Resolves DRIFT-001 recorded in echidnabot/.machine_readable/6a2/STATE.a2ml.
The dual-truth pattern (echidnabot tracked as regular files in this
parent repo + a `.gitmodules` entry that was never actually populated
as a submodule) caused silent divergence: edits made here didn't
propagate to github.com/hyperpolymath/echidnabot, and vice versa.

Decision (2026-04-25, Jonathan): standalone repo is canonical. Delete
the embedded copy entirely:

- `git rm -r echidnabot/` (157 files)
- `git rm .gitmodules` (file only contained the echidnabot entry)
- Removed cached .git/modules/echidnabot

Anyone needing echidnabot from this directory now clones the standalone:
  git clone git@github.com:hyperpolymath/echidnabot.git
  ../echidnabot

This matches the project_gitbot_fleet_dual_truth_pattern memory note —
silent dual-truth was the failure mode; explicit external clone is
the resolution.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath