docs: improve SemaPact discoverability metadata

[ElliotSun]

Summary

Tightens SemaPact's package metadata around its actual niche: ODCS data-contract lifecycle governance, schema evolution, breaking-change governance, GitOps, and Unity Catalog.

Included in this PR

• sharpen the package description to explicitly include ODCS, schema evolution, and breaking changes
• expand package keywords with both data-contract and data-contracts
• add high-intent discovery terms: schema-evolution, breaking-changes, unity-catalog, and data-products

Recommended GitHub UI changes (not editable safely through this PR)

Repository description:

Open-source lifecycle governance for ODCS data contracts: schema evolution, breaking-change detection, version policy, GitOps, and Databricks Unity Catalog integration.

Recommended repository topics:

• keep: data-contract, data-governance, data-mesh, databricks, gitops, odcs
• add: data-contracts, schema-evolution, breaking-changes, unity-catalog, data-products
• consider removing: metadata-management

Recommended README follow-up

The README content and architecture are already strong. I would keep the body intact and make only these narrow changes:

1. Change the tagline under # SemaPact from:

   Lifecycle governance for data contracts and enterprise semantics.

   to:

   Open-source lifecycle governance for ODCS data contracts, schema evolution, and governed data products.

2. Change Quick Start from a development-environment-first flow (uv sync --group dev) to an end-user installation-first flow once the published package path is confirmed, e.g. pip install semapact or uv tool install semapact.

3. Keep the contracthub CLI alias for compatibility if needed, but avoid presenting ContractHub as a second product name in public-facing docs while search engines are still reconciling the repository rename/transfer.

The README itself is intentionally not rewritten in this PR to avoid turning a clear technical README into SEO-heavy marketing copy.