[WIP] Review memory specification for better memory system

[Copilot]

• Analyze existing memory system implementation
• Create formal coworker/docs/memory-specification.md documenting the memory system architecture, formats, and lifecycle
• Fix bug in coworker-memory-generator.ps1: global type references undefined $prompt variable (line 213)
• Improve memory init context: include yearly memory alongside monthly + daily for richer context
• Improve monthly memory: replace unbounded daily-rollup appending with a single synthesized rolling summary
• Add memory validation: verify output file was created after generation
• Improve daily memory specification: add structured sections for task count and key decisions

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