fix(stack): keep Auth database and stack host connections alive

[jgoux]

TL;DR

stops local Auth and the stack host from opening a new connection for every request.

whats broken?

Auth keeps no idle Postgres connections unless an idle pool size is set, so every Auth request opened and closed its own database connection and left it in TIME_WAIT. A busy test suite could use up the macOS port range, the same way gateway writes did before #7075.

The stack host's HTTP client (readiness probes every 250 ms, log forwarding to Analytics) also used a non-keep-alive agent, so each call opened a new connection.

now fixed by:

• local Auth runs with a pool of 10 connections that stay open when idle, in both the stack and supabase start. No new config.toml keys.
• the stack host's HTTP client reuses connections and closes them after 4 s idle, before the shortest upstream keep-alive of 5 s.

ref:

• closes: Expose the Auth DB connection pool in config.toml (local Auth keeps no idle connections) #6981
• extends: fix(stack): pool gateway writes on keep-alive connections (CLI-2623) #7075