fix: remove duplicate proxy_read_timeout that crashes nginx on start

[ronibhakta1]

Problem

nginx fails to start: "proxy_read_timeout" directive is duplicate in 20-speech-server.conf:80. /synthesize includes proxy-pass.conf (which sets proxy_read_timeout 120s) and then sets 300s again in the same block. nginx rejects repeated directives in one block. The old container kept running an older config, so this only surfaced when the deploy recreated nginx, and the site went down.

Change

• Drop proxy_read_timeout from the shared proxy-pass.conf snippet.
• Set it per location: 120s in location /, 300s in /synthesize. Effective values are unchanged.

Verified

nginx -t in nginx:alpine with the rendered template: fails on main with the error above, passes with this change.

Follow-up worth considering: run this nginx -t in CI so config errors are caught before deploy.

[ronibhakta1]

Folded into #33 so the fix and the CI check that catches it land together (and #33 stays green).