fix: raise nginx's upload body size limit past its 1MB default

[JustSamuel]

Summary

Root cause of the "could not connect to server" reports on mobile photo uploads: nginx's compiled-in client_max_body_size default is 1MB, and frontend/nginx/default.conf never overrode it, even though the app's own upload caps go up to 50MB (video). nginx rejects the request with a 413 before the backend ever sees it -- and because the client is often still mid-upload when nginx closes the connection, browsers can surface that as a raw network failure rather than a clean HTTP error, which is what made this look like a connectivity problem instead of a size limit.

A real phone photo is almost always well over 1MB, so this failed reliably in production while never showing up in this session's own testing -- the Vite dev proxy used all session has no such limit at all, only the production nginx config does.

Root cause evidence

Reproduced locally with the real nginx image and the exact /api/ proxy config, pointed at the actual backend:

• 2MB file straight to the backend (bypassing nginx): 401 (bad token, but the full body reached the handler)
• Same file through nginx, unpatched: 413 Request Entity Too Large, 0 bytes uploaded
• Same file through nginx, with client_max_body_size 60m; added: 401, full body uploaded -- matches the direct-to-backend result
• 70MB file through the patched config: still cleanly 413 -- the raised limit is bounded, not disabled

Test plan

• Reproduced the bug and verified the fix with the real nginx image (see above)
• Change is a single config line; no application code touched

[github-actions]

Coverage Report for frontend

Status	Category	Percentage	Covered / Total
🔵	Lines	88.35%	1312 / 1485
🔵	Statements	85.91%	1440 / 1676
🔵	Functions	83.3%	454 / 545
🔵	Branches	81.39%	884 / 1086

File Coverage

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