fix(deploy): resolve curl from PATH in Git Bash

[luojiyin1987]

Summary

• Resolve curl from PATH in the deployment scripts.
• Support an explicit CURL=/path/to/curl override.
• Check curl only when host-side LLM verification runs.
• Report curl exit codes and preserve short error details.

Root cause

start-memory-core.sh and verify.sh assumed that curl exists at /usr/bin/curl.
Git Bash can provide curl at a different path.
The scripts also converted command failures to HTTP 000 and discarded stderr.

User impact

Windows Git Bash can now use curl from PATH.
Linux and macOS keep their existing PATH behavior.
Operators can set an explicit curl executable through CURL.
Offline verification with --skip-llm does not require curl.

Validation

• bash -n deploy/global-images/start-memory-core.sh deploy/global-images/verify.sh
• shellcheck -x deploy/global-images/_lib.sh deploy/global-images/start-memory-core.sh deploy/global-images/verify.sh
• Verified that --skip-llm ignores CURL=/definitely/missing.
• Verified a clear missing-curl error when LLM verification runs.
• Verified exit-code output with CURL=/bin/false.
• Verified that .env can override an inherited CURL value.
• Verified default CURL=curl resolution on Linux.

Windows Git Bash validation remains pending.

The shell changes and failure paths have been validated on Linux.
An end-to-end Windows Git Bash test is still requested from the original reporter.

Fixes #655

[Maxwell-Code07]

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