fix(nginx): proxy /1/ prefix (catalogStats, funnelCounts) to django

[WilfordGrimley]

Summary

• Add a location /1/ proxy block to docker/nginx/nginx.conf so /1/catalogStats/ (stats page) and /1/funnelCounts/ (homepage participation graph) reach the Django API instead of 404ing at nginx. The GitHub Pages frontend already requests these URLs; only the API origin's nginx routing was missing.
• Add a deployment note to docs/features/catalog-stats.md documenting the nginx /1/ routing requirement (this change affects what a user sees).

Test plan

• nginx -t in the prod mpcautofill_nginx image on the compose network with the modified config mounted — syntax ok / test successful
• git diff confirms the change is exactly the 4-line location block
• Manual: after deploy, curl https://api.proxyprints.ca/1/catalogStats/ returns the warm JSON blob and the /stats page renders — deferred to post-deploy verification (deploy is owner-run)
• CI — not watched by this session per dispatch convention

Task-end checks (from the catalog repo CLAUDE.md — apply explicitly, they are not auto-loaded):

• wiki: deployment note added to docs/features/catalog-stats.md — nginx must route /1/ to django (this change affects what a USER sees). docs_lint.py --strict clean; catalog-stats.md already has a MANIFEST row and is not in the wiki-publish map, so no MANIFEST/publish-map change needed.
• Extractable primitives: N/A — nginx config only, no code primitive created/destroyed
• Docs: deployment note added to docs/features/catalog-stats.md (the one existing feature doc that governs this surface); nginx prefix routing is not otherwise enumerated in repo docs, so no other doc file update needed