feat: add Mimir workspace packages

[jb-thery]

Summary

• Move the core @jcode.labs/mimir package into packages/mimir and keep the repository root as a private pnpm workspace orchestrator.
• Add @jcode.labs/mimir-tts as a sibling package for Python-free local WAV rendering through Transformers.js.
• Add kb audio, update docs/agent guidance, release artifacts, CI, and protected npm publishing for the two-package workspace.
• Keep the synthetic example under the core package and keep generated Mimir state ignored.

Validation

• pnpm validate
• git diff --check
• secret pattern scan over tracked workspace files, excluding generated dist and release artifacts
• release artifact check: @jcode.labs/mimir tarball depends on @jcode.labs/mimir-tts as 0.4.0, not workspace:*

Release notes

After merge to main and green CI, use the protected Publish npm workflow with version 0.4.0. The workflow publishes @jcode.labs/mimir-tts first, then @jcode.labs/mimir.