feat: add memory-management skill

[thomas-chen-glean]

Summary

• Adds the memory-management skill from askscio/skills, adapted for the cursor-plugins frontmatter convention
• Provides playbooks for session continuity, style adaptation, and broad context retrieval using memory_schema and read_memory MCP tools
• Updates the Glean plugin README with the new skill entry

Compatibility with incoming MCP memory changes

Reviewed against three in-flight PRs on the MCP memory server. No skill changes were needed:

PR	Change	Impact on skill
askscio/scio#239670	Require explicit memory_source on writes; add VSCode/Shared sources	None — the skill's core rule #1 ("treat memory_schema as the runtime contract") means agents discover write requirements from the schema, not hardcoded assumptions
askscio/scio#239709	Echo deleted entry metadata in delete response	None — transparent server-side improvement
askscio/scio#239714	Reject MCP TextContent arrays in content field	None — the skill already implies content is plain text; the schema-first approach handles validation errors gracefully

Test plan

• npm run validate passes
• Verify skill loads correctly in Cursor with the Glean plugin installed
• Verify memory_schema and read_memory work as described in the skill playbooks

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