Add descriptions to all operations and parameters across constructs

[arjunmehta-git]

Context

Many operations and parameters in the schema constructs lack `summary`, `description`, or both.

Problem

• Operations without summaries produce blank entries in API documentation
• Parameters without descriptions are opaque to API consumers and generated code users
• This is a documentation completeness gap

Proposal

Audit all `api.yml` files and add:

1. `summary` (one-line) and `description` (detailed) to every operation
2. `description` to every path, query, and header parameter
3. Pair this with the new validator rules (Validator: add operation and parameter description checks (Rules 45-46) #718) to enforce going forward

Scope

Touches every construct with endpoints (~20 `api.yml` files). Large but mechanical — each operation needs a sentence or two.

References

Identified in schema validator audit — Section 5 items #4 and #5.