feat(orders): add "Devis" button + preview modal to every order detail page

[AntoinePoindron]

Summary

The "Voir le devis" preview modal already existed on the request detail pages on both sides. This PR surfaces it on the order detail pages too so:

• a client can re-read the quote that's been turned into an order,
• the caterer can re-open it from the order context,
• the super_admin gets the same observer-view.

Validated end-to-end manually by @AntoinePoindron before opening this PR.

What changed

Surface	Where	Download route
client/orders/detail.html	"Devis" ghost-pill on the Devis accepté sidebar card	client.quote_pdf (added in #44)
caterer/orders/detail.html	"Devis" ghost-pill in the Detail du devis section header	caterer.quote_pdf
admin/orders/detail.html	"Devis" ghost-pill in the Montants section header	admin.quote_pdf (new in this PR)

Each modal mirrors the per-quote one on client/requests/<id>: same _pdf_preview.html partial, same close-X + Télécharger pair in the header.

⚠️ Stacked on #44

Base branch: feat/quote-preview-download-button (PR #44). The client side relies on client.quote_pdf from that PR. Merge order: #44 → this one, this one rebases onto main automatically.

Backend

• New GET /admin/quotes/<q_id>/pdf route in blueprints/admin.py. super_admin sees every quote, no scope check needed; same _MAX_PDF_LINES = 500 cap as the other roles.
• Each order_detail handler now calls services.quotes.build_pdf_preview(order.quote, order.quote.quote_request, order.quote.caterer) and passes the dict + meal_type_labels to the template. Returns None (button hidden, modal not rendered) if the order's quote has no line items — defensive against legacy rows.

What is NOT changed

• services.quote_pdf.render_quote_pdf — same signature, same template.
• The existing per-quote modals on the request detail pages.
• Permission checks: each role's PDF download is scoped to that role's view (caterer → caterer_id, client → company_id, admin → unscoped).

Test plan

• 198 existing tests pass.
• Manually validated by user across the three roles: button shows, modal opens, download works.
• Once feat(quote-preview): add "Télécharger" button to every quote-preview modal #44 + this merge: smoke on staging — confirm the Stripe-invoice flow on the same page still works (no regression on the existing layout).

🤖 Generated with Claude Code