fix(config): support list options from environment variables

[lovasoa]

Fixes #1383

Summary

Register every list-valued AppConfig option with the config crate environment parser. Environment variables now accept space-separated lists for sqlite_extensions, oidc_protected_paths, oidc_public_paths, and oidc_additional_trusted_audiences. The configuration reference documents the environment syntax.

Stripped verification logs

$ SQLPAGE_OIDC_PROTECTED_PATHS="/user /admin" SQLPAGE_OIDC_PUBLIC_PATHS="/health /login" SQLPAGE_OIDC_ADDITIONAL_TRUSTED_AUDIENCES="audience_one audience_two" ./target/debug/sqlpage
Loaded configuration: ... oidc_protected_paths: ["/user", "/admin"], oidc_public_paths: ["/health", "/login"], oidc_additional_trusted_audiences: Some(["audience_one", "audience_two"]) ...
SQLPage v0.45.0 started successfully!

Full cargo test passed: 175 unit tests and 73 integration tests. cargo clippy --all-targets --all-features -- -D warnings and cargo fmt --all -- --check also passed.