CP-14535 - Deduplicate signature pad canvas sizing across the four pads

[bernardodsanderson]

CP-14535 - Deduplicate signature pad canvas sizing across the four pads

What

Extracts the canvas resize-on-orientation lifecycle (setup / teardown / resizeCanvas plus the double-rAF debounce handler) that PR #79 (CP-14191) copy-pasted into four signature pads into one shared module, app/javascript/submission_form/canvas_sizing.js, following the existing crop_canvas.js shared-module convention. All four pads now call the same setupCanvasSizing(options) with their own options object:

• Vue pair (submission_form/signature_step.vue, initials_step.vue): width-derived height via their existing canvasHeightForWidth (3:1 / 4.5:1), uniform stroke ratio, persistent IntersectionObserver (re-sizes when a minimized/hidden field becomes visible), typed-signature re-render after resize.
• Custom elements (draw.js <draw-signature>, elements/signature_form.js <signature-form>): height read from the live parent box, per-axis stroke ratios.

Net −221 lines (5 files, +175/−396). The "Double rAF: orientationchange fires before layout has settled" comment now lives exactly once — it had drifted into only the two Vue files, the drift flagged in the #79 review.

Why

After CP-14191 the next tweak to canvas sizing would have to land in four places, and drift was already visible (the double-rAF comment existed only in the Vue pair). This is the maintainability follow-up Paul suggested in the PR #79 review: pull the shared lifecycle into one place so future fixes land once. Pure refactor with zero behavior change — landscape/portrait finger alignment, stroke preservation on rotation, typed-text re-render, and teardown on unmount are preserved exactly; the intentional per-stack differences (height source, ratio style, Vue-only observers/typed restore) are parameterized options instead of divergent copies.

How to test

• bundle exec rspec spec/system/signing_form_spec.rb — draw + typed signature flows (cuprite, js_errors: true); passes 24 examples, 0 failures on this branch.
• yarn eslint — clean on the touched files.
• Manual orientation check (no automated coverage exists): start the app, open a signing form (/s/:slug) and the mobile full-page draw pad (/d/:slug/sign), draw a stroke, rotate landscape ⇄ portrait — strokes should stay under the finger and survive rotation; typed signatures re-render after rotation; no console errors.

https://careerplug.atlassian.net/browse/CP-14535

[jewls618]

Looks like a clean clean-up 👍