V1: Document available DHL parcel box retrofit components

[mastertape]

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

Document all available parts before mechanical or firmware decisions are made.

Acceptance criteria:

• Photos of DHL parcel box, door, lock area, inside space and cable paths are added or linked.
• Existing lock unit is documented from outside and inside where possible.
• Keypad/RFID/fingerprint modules are listed with product names, voltages and interfaces.
• ESP board candidate is documented.
• Relay/MOSFET/driver modules are listed.
• Battery, solar and charger parts are listed.
• Door sensors, tamper contacts and cable glands are listed.
• Unknown parts are marked as unknown instead of guessed.

Notes:
This issue should collect the real component inventory that arrives over the next days.