Add AccInt plugin

[maxbaluev]

Summary

• Add AccInt as a Memoh plugin manifest.
• Register the local stdio MCP server with an ACC_DB variable for the user-owned database path.
• Keep the entry scoped to AccInt's memory, commitment tracking, and outcome-feedback capabilities.

Validation

• Duplicate gate: no existing AccInt entry found under plugins/ or skills/.
• YAML parse check passed for plugins/accint/plugin.yaml.
• Link check: https://github.com/maxbaluev/accreted-intelligence returns HTTP 200.
• git diff --check
• bun install --frozen-lockfile
• bun run build