v1.0.0 — Polaris Stable

Polaris Stable — the first public release. No new features: this is the
graduation pass over everything built across v0.1–v0.12. The full from-scratch NLP
lifecycle — data → tokenization → collation → models (a from-scratch transformer) →
training → evaluation → experiment tracking → pretrained embeddings →
self-supervised pretraining → deployment — is runnable end to end, documented, and
frozen under semantic versioning.

Changed

• API freeze. The public API is each module's __all__; these surfaces are now
  stable under semver. The top-level polaris package intentionally stays minimal
  (only __version__) so importing it is cheap and needs no optional extras.
• Documentation pass. Every implemented module now has an accurate README (fixed
  the core, models, evaluation, experiments, and utils stubs; added
  collation and embeddings). The top-level README gains Installation and
  Quickstart sections, and the badges/intro reflect the stable release.
• CI hardening. The workflow now runs a matrix — Python 3.12 & 3.13 on Ubuntu
  and macOS — with the fail_under = 90 coverage gate enforced.