feat(fusion-tsdoc-readme): add reusable TSDoc and README documentation skill

[odinr]

Why

No reusable skill exists for systematic TSDoc and README documentation passes across packages. The workflow was proven effective across a 41-package documentation sprint on equinor/fusion-framework (equinor/fusion-core-tasks#599) but required bespoke prompts every time — no consistent quality bar, no orchestration guidance, and no review council.

Current behavior

• TSDoc enforcement exists only as a sub-concern of fusion-code-conventions
• No skill for running systematic documentation passes across multiple packages
• No README structure standard or template for package documentation
• Each documentation session reinvents what "good TSDoc" and "good README" look like

New behavior

New fusion-tsdoc-readme orchestrator skill with:

• SKILL.md (180 lines) — repo-aware conventions discovery, TSDoc pass, README pass, review council, and multi-package orchestration workflow
• agents/tsdoc.agent.md — scans exports, classifies documentation state, and improves TSDoc
• agents/readme.agent.md — assesses README structure and rewrites to consistent format
• agents/reviewer.agent.md — four-dimension review council (intent extraction, code comprehension, user-facing quality, retrieval fitness)
• references/readme-structure.md — standard README section structure
• references/orchestration.md — multi-package batching, context isolation, and token budget strategy
• assets/readme-template.md — copy-pasteable README scaffold

Delegates TSDoc convention rules to fusion-code-conventions (declared in metadata.skills) rather than duplicating them.

References

• Issue(s): Resolves equinor/fusion-core-tasks#702
• Related PR(s): —
• Docs / specs: Prior art from equinor/fusion-core-tasks#599 (41-package doc pass)

Reviewer focus

• Start here (files/areas): skills/fusion-tsdoc-readme/SKILL.md
• Verify these behavior changes: Skill appears in npx -y skills add . --list output, passes validate:skills and validate:ownership
• Risky or security-sensitive parts: None — read-only documentation workflow skill, no scripts

Self review checklist

• I scoped this PR to one clear purpose.
• I followed CONTRIBUTING.md.
• I did not include secrets, credentials, or sensitive data.
• I reviewed my own diff for clarity and unintended changes.

[github-actions]

Changeset summary

Detected 1 changeset file(s):

.changeset/add-fusion-tsdoc-readme-skill.md:

---
"fusion-tsdoc-readme": minor
---

Add reusable skill for systematic TSDoc and README documentation passes

- Orchestrator SKILL.md with TSDoc pass, README pass, and review council workflow
- Three agents: tsdoc (export scanning and TSDoc improvement), readme (structure assessment and rewrite), reviewer (four-dimension quality review)
- References for README structure guide and multi-package orchestration strategy
- README template asset for consistent package documentation

Resolves equinor/fusion-core-tasks#702