Update reconciliation.md to reflect actual implementation

Rewrite the design document based on what was actually implemented,
lessons learned during CI validation, and guidance for future work.
Key additions: section 7 (lessons learned) with the 7 pitfalls
encountered, updated architecture reflecting that ensureNetworks/
ensureVolumes remain unchanged, and streamlined implementation guide.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

Author: ndeloof