Fix CI plugin distribution overrides masking proto upgrade behavior

[Copilot]

The failing run_legacy jobs were not caused by the removed timeout vars; they were caused by CI still forcing debug/url-based plugin distribution across all Rust jobs while the CLI also coerced MOON_PLUGINS_USE_URL_DIST into PROTO_PLUGINS_USE_URL_DIST=true on mere presence. That combination masked the default ghcr.io path introduced by the proto/warpgate upgrade and made CI exercise the wrong bootstrap path.

• What changed

  • Removed the temporary plugin distribution overrides from Rust CI so test jobs use the default registry-backed resolution path.
  • Fixed moon → proto env propagation so the proto flag preserves the actual boolean value instead of treating presence as true.
  • Kept the plugin bootstrap path aligned between moon and proto so CI now validates the intended post-upgrade behavior.

• Why this matters

  • CI was validating a debug-only URL distribution path instead of the new default registry flow.
  • Falsey values like MOON_PLUGINS_USE_URL_DIST=false were still being converted into PROTO_PLUGINS_USE_URL_DIST=true, making local behavior and CI behavior diverge.

• Behavioral change

  • Before, any presence of MOON_PLUGINS_USE_URL_DIST forced proto into URL mode.
  • Now, proto only follows the explicit boolean value.

if let Some(value) = bag.get("MOON_PLUGINS_USE_URL_DIST") {
    bag.set("PROTO_PLUGINS_USE_URL_DIST", value);
}