Fix RFC 0001 origin/catalog contract examples to match CLI

[sakul-learning]

Context

PR #27 (docs(013): add RFC 0001 for the skillrig mise backend plugin) was merged with two docs/contract mismatches identified by the automated review.

Review follow-up comment: #27 (comment)

Issues to fix

1. .skillrig-origin.toml convention key mismatch

RFC 0001’s origin-side contract example documents:

skillrig-convention = 1

The current CLI parser and fixtures use:

convention_version = 1

If an origin follows the RFC literally, the current CLI will treat the convention version as missing/zero and fail the convention gate.

2. index.json.skills shape mismatch

RFC 0001 currently shows:

"skills": { /* unchanged */ }

The implemented catalog contract is an array:

Skills []CatalogEntry `json:"skills"`

Existing generated/golden catalogs use:

"skills": [ ... ]

Suggested fix

Update RFC 0001 so it matches the current CLI contract:

• Use convention_version = 1 in .skillrig-origin.toml examples.
• Use "skills": [ /* unchanged */ ] in index.json examples.

If either mismatch is intentional as a future migration, document it explicitly and include the matching CLI implementation, tests/fixtures, design-doc compatibility notes, and convention-version handling.

Acceptance criteria

• RFC 0001 no longer documents skillrig-convention as the current origin convention key unless a migration is implemented.
• RFC 0001 no longer documents index.json.skills as an object unless a catalog schema migration is implemented.
• Any updated examples align with existing CLI fixtures or updated fixtures/tests if the contract intentionally changes.