fix: three errors that ended with the wrong exit code

Found compiling the environment-variable table for AGENTS.md:
- A REVIEW_GATES_MEM_RESERVE_MB that is no number threw
  std::invalid_argument, which nothing caught: the process aborted where
  it should end with a ValueError, exit 1. nan and inf were an unchecked
  cast. They raise ValueError / OverflowError now; a value past int64
  saturates.
- An env file that is not UTF-8: `run` ended with exit 1 where its
  preflight should stop it (exit 3), and `seats` parsed the raw bytes. Both
  read it as strict UTF-8 text now.
- A broker address with a port past 65535 was cut to 16 bits; it is an
  OverflowError now, uncaught (exit 1).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/Commands/main.cpp

@@ -212,10 +212,13 @@ echo '{"type":"result","subtype":"success","is_error":false,"result":"ok","total
               json.out.substr(0, 600) + json.err);
         const Process::Captured none = Self({"seats"}, base / "plain", withFake);
         const Process::Captured noFile = Self({"seats", "--env-file", "missing.env"}, base / "plain", withFake);
-        Check("seats: no seat configured is exit 1 with what it looked for; a missing env file is exit 1 with the read error",
+        Write(base / "plain" / "bad.env", std::string("\xff\n", 2));
+        const Process::Captured badFile = Self({"seats", "--env-file", "bad.env"}, base / "plain", withFake);
+        Check("seats: no seat configured is exit 1 with what it looked for; a missing env file and one that is not UTF-8 are exit 1 with the read error",
               none.returnCode == 1 && none.out.starts_with("no seat configured (CLAUDE_CODE_OAUTH_TOKEN1..6 / ANTHROPIC_API_KEY1..6; --local probes your own login)")
-                  && noFile.returnCode == 1 && noFile.err.contains("FileNotFoundError: [Errno 2] No such file or directory: 'missing.env'"),
-              none.out + noFile.err);
+                  && noFile.returnCode == 1 && noFile.err.contains("FileNotFoundError: [Errno 2] No such file or directory: 'missing.env'") && badFile.returnCode == 1
+                  && badFile.err.contains("UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 0: invalid start byte"),
+              none.out + noFile.err + badFile.err);
 
         // browser: its usage (an install fetches from npm).
         const Process::Captured noAction = Self({"browser"}, base);