Add Prindle microfluidic device source files

[marpaia]

Purpose

This PR isolates the large Prindle device source artifacts from code and prose review. It depends on #4 only to preserve the stack order and contains no solver, coupling, or tutorial implementation.

Contents

• docs/tutorials/devices/README.md
• docs/tutorials/devices/prindle.dwg
• docs/tutorials/devices/prindle.dxf

The 413,362-line DXF remains in its own PR so it cannot obscure review of walls, native flow solvers, coupling, or tutorials.

Provenance and interpretation boundary

• Gonzalo Vidal provided these files to Mike Arpaia for inclusion and redistribution in this DRAGGON Lab project. DRAGGON Lab is Gonzalo Vidal's research group at the University of Bristol. The adjacent README records that provenance.
• PR Add microfluidic device and biology tutorials #6 treats physical scale as a source-specific inference: raw dimensions of 0.100 and a row pitch of 0.125 correspond to the published 100 micrometer trap dimension plus 25 micrometer spacing under a 1,000 micrometers-per-drawing-unit conversion. The $INSUNITS=1 metadata is not treated as an authoritative physical-unit declaration.
• PR Add microfluidic device and biology tutorials #6 does not derive cavity walls or layer thicknesses from these assets and does not claim that they are the exact fabrication revision used in the publication. The unplaced Layer-5 block geometry remains without a physical-layer assignment because no process map accompanies the files.

Stack

PR 4 of 5.

Base: #4 (marpaia/microfluidics-experimental-coupling).

Next: #6 (marpaia/microfluidics-tutorials).

Rebased asset-only head: a5b1b73.