docs: comprehensive README and architecture documentation

[NOVA-Openclaw]

Summary

Rewrites the top-level README to document all scripts in the repository, not just gdrive-sync.sh. Also adds a new ARCHITECTURE.md that describes how the semantic memory pipeline works end-to-end.

Changes

README.md — Complete rewrite:

• Table of contents with all sections
• Memory Pipeline scripts (extract-memories, embed-memories, cron wrapper)
• Search & Recall scripts (semantic-search, proactive-recall, recall-benchmark)
• Maintenance scripts (decay-confidence)
• Utilities (gdrive-sync)
• Git Security hooks (install-hooks, pre-commit-template)
• Agent Chat Channel plugin (summary + link to existing detailed README)
• Prerequisites section with all dependencies
• Updated project reference from Clawdbot → OpenClaw

ARCHITECTURE.md — New file:

• Data flow diagram showing the full memory pipeline
• Detailed description of each stage (Extraction → Embedding → Recall → Maintenance)
• Database schema reference
• Configuration and environment variables
• Integration points with NOVA ecosystem
• Extending the pipeline
• Troubleshooting guide

Motivation

The previous README documented only 1 out of 10+ scripts. New users had no way to understand what the repo contained or how the scripts related to each other. This PR makes the repo self-documenting.

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Generated during D100 idle task — Roll #96: "Have Scribe document an undocumented project"