[codex] add mem0 memory plugin

[furukama]

What changed

• add a bundled mem0-memory external memory provider under plugins/mem0-memory
• wire prompt-time Mem0 profile/search recall, turn sync, native memory-write mirroring, /mem0 commands, and mem0_* tools
• add targeted unit coverage for config security, prompt injection, tool/command behavior, turn sync, and native memory mirroring
• add Mem0 plugin docs and update extensibility navigation/README references
• add Tips & Tricks and Troubleshooting sections across all memory-plugin docs

Why

HybridClaw already ships memory plugins for Honcho and MemPalace, and the local example repos also include a Mem0 integration pattern. This change brings Mem0 in as a first-class bundled memory provider so operators can use Mem0 cloud memory with the same plugin lifecycle, command surface, and documentation flow as the other external memory systems.

Impact

• operators can install and enable mem0-memory locally with a managed plugin flow
• prompt recall can pull Mem0 profile/search context without disabling built-in memory
• explicit saved facts from native memory writes can be mirrored into Mem0 for later recall
• maintainers get a documented setup path and consistent troubleshooting guidance across all memory-plugin docs

Validation

• npm run format
• ./node_modules/.bin/vitest run --configLoader runner --config vitest.unit.config.ts tests/mem0-memory-plugin.test.ts
• doc structure check confirming each docs/development/extensibility/*memory*.md page now contains both Tips & Tricks and Troubleshooting

Notes

• local examples checked before implementation: ~/examples/hermes-agent/plugins/memory/mem0 plus ~/examples/hybridclaw/plugins/{honcho-memory,mempalace-memory,gbrain}
• repo-wide npm run lint was not used as the final gate in this /tmp worktree because existing module-resolution issues in that environment were unrelated to the Mem0 diff