fix(hermes): archive removed local memories

[wbugitlab1]

Summary

• Update Hermes on_memory_write so add/update events are skipped instead of mirrored into agentmemory.
• Archive non-blank remove events through existing /agentmemory/remember with archive wording, stable external_id, metadata, tags, session/project, and agent identity.
• Document the new behavior and AGENTMEMORY_HERMES_ARCHIVE_REMOVES=0 opt-out.

Closes #335

Verification

• corepack pnpm test test/integration-plaintext-http.test.ts test/hermes-plugin.test.ts (post-merge): 2 files, 27 tests passed.
• semgrep scan --config p/default --error --metrics=off .: 0 findings.
• gitleaks protect --staged --redact: no leaks found before commit.
• git diff --check: clean before commit.

Notes

• Full corepack pnpm test was attempted twice before PR prep and failed only in test/codex-sdk-provider.test.ts due a 2000ms Codex CLI timeout in full-suite context; the same test file passed in isolation with 3 tests.