Complete API collection content for docs

[roncodes]

Summary

Completes the content metadata needed by the generated API reference docs.

This PR adds:

• missing body parameter sidecars for every JSON-body request
• canonical 2xx response examples for every request
• resource object sidecars for every resource folder
• tightened endpoint descriptions where generated or placeholder copy was still weak

Coverage audit

Final audit from postman/collections:

• Requests: 222
• Resource folders: 40
• .params.yaml files: 95
• .queryParams.yaml files: 45
• .example.yaml files: 253
• .resources/object.yaml files: 40
• Missing JSON-body params: 0
• Missing usable 2xx response examples: 0
• Missing resource object files: 0
• URLs with embedded query strings: 0
• Known stale/generic description patterns: 0

Commit structure

Endpoint content commits:

• Complete Fleetbase API endpoint content
• Complete Core API endpoint content
• Complete Ledger API endpoint content
• Complete Storefront API endpoint content
• Complete Integrated Vendor Flow endpoint content

Resource object commits:

• Add Fleetbase API resource object metadata
• Add Core API resource object metadata
• Add Ledger API resource object metadata
• Add Storefront API resource object metadata

Follow-up polish:

• Polish generated endpoint descriptions

The Integrated Vendor Flow collection has no resource subfolders, so it has no resource-object commit.

Verification

• YAML parse for postman/collections/**/*.yaml
• node scripts/validate-collections.js
• pnpm postman:lint
• git diff --check
• POSTMAN_COLLECTIONS_DIR=/Users/ron/Development/fleetbase/postman/postman/collections node scripts/generate-api-docs.mjs from fleetbase.io
• Spot-checked content/docs/api/fleetbase/places.mdx
• Spot-checked content/docs/api/storefront/cart.mdx

Note: Postman CLI is not installed locally, so scripts/lint-collections.sh ran the repository validator and skipped Postman CLI schema lint as designed.