Cardano Updates

Add AGENTS.md as the cross-tool entry point and
skills/cardano-balance-transaction-guide/SKILL.md (agentskills.io
layout) with repository map, build/test commands, code-navigation
pointers, balanceTx usage, and an answering-questions section. All
commands and module/symbol references are verified against the source.

- Restructure into the standard section order (What is this,
  Architecture, Install, Quickstart, Usage, Documentation, Development).
- Correct the supported eras from Babbage/Conway to Conway/Dijkstra,
  matching the RecentEra GADT (RecentEraConway, RecentEraDijkstra).
- Add a mermaid architecture diagram of the balancing pipeline.
- Replace the unverified test count with a description of the suite.
- Document the just/flake commands that CI actually runs, and the
  source-repository-package consumption path.
- Refine the Sign module description (size/fee estimation, not signing).
- Point AI agents at AGENTS.md.

- Update index/architecture/modules pages from Babbage/Conway to the
  actual RecentEra coverage (Conway and Dijkstra).
- Fix mermaid diagrams: replace literal \n with <br/> so node labels
  render as line breaks instead of backslash-n.
- Correct the Tx and Sign module descriptions to match their exports.
- Align getting-started build/test/docs commands with the just recipes
  and the mkdocs flake CI uses; drop the unverified 268-test count.
- Add a light/dark palette toggle and site_url to mkdocs.yml.

Add AGENTS.md as the cross-tool entry point and
skills/cardano-balance-transaction-guide/SKILL.md (agentskills.io
layout) with repository map, build/test commands, code-navigation
pointers, balanceTx usage, and an answering-questions section. All
commands and module/symbol references are verified against the source.

- Update index/architecture/modules pages from Babbage/Conway to the
  actual RecentEra coverage (Conway and Dijkstra).
- Fix mermaid diagrams: replace literal \n with <br/> so node labels
  render as line breaks instead of backslash-n.
- Correct the Tx and Sign module descriptions to match their exports.
- Align getting-started build/test/docs commands with the just recipes
  and the mkdocs flake CI uses; drop the unverified 268-test count.
- Add a light/dark palette toggle and site_url to mkdocs.yml.

- Restructure into the standard section order (What is this,
  Architecture, Install, Quickstart, Usage, Documentation, Development).
- Correct the supported eras from Babbage/Conway to Conway/Dijkstra,
  matching the RecentEra GADT (RecentEraConway, RecentEraDijkstra).
- Add a mermaid architecture diagram of the balancing pipeline.
- Replace the unverified test count with a description of the suite.
- Document the just/flake commands that CI actually runs, and the
  source-repository-package consumption path.
- Refine the Sign module description (size/fee estimation, not signing).
- Point AI agents at AGENTS.md.