fix(acp): harden grok startup environment and npx recovery

[kaizhou-lab]

Summary

• strip SSL_CERT_FILE and SSL_CERT_DIR from agent subprocess environments while preserving NODE_EXTRA_CA_CERTS
• repair managed npm _npx cache entries after ACP startup/handshake failure by computing npm's package hash from the actual CommandSpec and deleting only that single entry when it exists
• keep stderr-based _npx path detection as a fallback for startup failures where the managed command cannot be computed
• classify provider send failures as retryable provider network errors without automatic conversation replay

Verification

• cargo fmt --all -- --check
• cargo test -p aionui-ai-agent npx_cache_repair
• cargo clippy -p aionui-ai-agent -- -D warnings
• GitHub CI for PR fix(acp): harden grok startup environment and npx recovery #662 passed: Clippy, Format, Migration Immutability, Detect dependency changes, Test

Notes

• AionUi changes were not included; this fix is contained in AionCore.
• ACP conversation startup and test-connection lifecycle remain separate; only npm _npx cache repair logic is shared.
• The _npx repair does not clear the whole _npx cache; it clears only the computed entry for the failed command, then retries once.