v1.15.9

## Summary

- Fixes MCP project resolution so `mem_save(project=...)` can target the intended workspace only when that project is backed by known context.
- Prevents arbitrary or typoed project names from creating new memory buckets.
- Adds monorepo-friendly `.engram/config.json` detection for independent subprojects.

## Details

- Validates explicit project selections against existing store/session/config context.
- Fails loudly for unknown projects, session mismatches, blank project values, ambiguous recovery mistakes, and project-name normalization collisions.
- Keeps `mem_update` from accepting hidden raw project retargets.
- Aligns MCP docs, OpenSpec, and runtime tool descriptions with the current 19-tool contract.

## Verification

- `go test ./...`
- `go test -cover ./internal/mcp ./internal/project`