fix(expense): constrain receipt preview image size

Problem

On Dodock/HRMS v5, opening an Expense with a high-resolution image attached as the receipt renders the "Aperçu" (preview) at the image's native pixel size (e.g. ~3000px tall for a ~4000x3000 smartphone photo), stretching the form across several screens.

Root cause

preview_file in expense.js injects <img class="img-responsive">, relying on Bootstrap 3's .img-responsive to cap the size. On the v5 desk that class no longer applies max-width: 100%; height: auto. Separately, the receipt field moved from Attach Image (which had a max-height: 512px constraint) to Attach in the v4->v5 migration, removing the other constrained-preview path. Dodock's own ControlImage already works around the same class loss inline, but this preview doesn't use ControlImage.

Fix

Add explicit inline styling (max-width:100%; max-height:512px; height:auto; object-fit:contain) to the preview <img>, matching the convention already used in attach_image.js, plus a click handler to open the full-resolution image in a new tab.

Closes #58 (closed)