fix(hermes): install durable user plugin link

[YOMXXX]

Summary

• fixes Hermes install only links memory_tencentdb into checkout tree; plugin can disappear after update and silently detach memory #167 by installing memory_tencentdb into both Hermes discovery locations
• keeps the existing checkout-tree link for compatibility and adds the durable $HERMES_HOME/plugins/memory_tencentdb user-scope link
• honors HERMES_HOME overrides and verifies provider source files before linking
• refuses to overwrite non-symlink plugin targets and prints link summaries after install

Why

The installer previously linked only into $HERMES_AGENT_DIR/plugins/memory/memory_tencentdb. Hermes checkout updates can remove that tree while memory.provider: memory_tencentdb remains configured, silently detaching TencentDB memory. This PR is a clean, tested replacement for the older unstable #170.

Verification

• npx vitest run src/install-hermes.test.ts (RED before fix, green after)
• bash -n scripts/install_hermes_memory_tencentdb.sh
• npm test
• npm run build
• git diff --check

[Maxwell-Code07]

Awesome work! 13 fixes in one batch covering Gateway hardening, embedding compatibility, Hermes memory injection, offload stability, and pipeline optimization — a very productive cleanup session 👏

We'll review and merge them one by one 🚀