V1: Evaluate DHL parcel box lock retrofit strategies

[mastertape]

Roadmap reference: docs/roadmap/dhl-paketkasten-retrofit-v1.md

Evaluate how the first DHL parcel box retrofit should handle the old lock unit and the new lock mechanism.

Acceptance criteria:

• At least three lock strategies are compared: remove, gut/reuse housing, adapt original mechanics, or replace with new lock.
• Each strategy notes required mechanical work, security implications and emergency-opening behavior.
• Lock actuation type is proposed: solenoid, motor lock, cabinet lock, relay-controlled module or OpenParcelLock prototype.
• Fail-safe/fail-secure behavior is described.
• Internal/protected placement of controller and lock wiring is documented.
• A first preferred prototype direction is selected or blockers are listed.

Non-goal:
No final certified lock design is required in this issue.

[mastertape]

Relevant official DHL baseline reference added to the V1 roadmap:

• docs/roadmap/dhl-paketkasten-retrofit-v1.md
• DHL video: https://www.youtube.com/watch?v=jXzvwI64qbM

Project-relevant summary: DHL demonstrates a simple manual conversion path: open the original mechanism, remove batteries so the electronic latch remains open, mount a mechanical combination lock, and store the code in the alternative drop-off location instructions. For this issue, treat that as the baseline mechanical fallback/contrast point. V1 should decide whether OpenParcelBox reuses, guts, removes or replaces the original lock unit while preserving the same practical insight: keep the physical box useful, replace the closed control layer.