refactor: consolidate unique helpers

[GRAMMAC1]

Summary

• Centralize generic unique in core text utilities.
• Add uniqueNonEmptyStrings for existing call sites that relied on empty-string filtering.
• Replace duplicate core parser and aggregate implementations with shared utilities.
• Reuse the core non-empty string helper from MCP tool utilities while preserving the existing MCP unique export.

Validation

• pnpm verify
• pre-commit Biome check during commit

Note: sandboxed pnpm verify passed check/lint/typecheck/tests but failed at the harness step because tsx could not create its IPC pipe under the sandbox. The non-sandbox rerun passed.