[DOCS-5092] [CLI] Merge does not handle exteral $ref's

[philsturgeon]

When running merge command on

speakeasy merge -s ~/src/train-travel-api/openapi.yaml -s ~/src/examples-examples/oas3.yaml

This creates the following error:

component ./models/todo-full.v1.json does not exist in the specification

Full output:

  Values for 1 field has been supplied ✔

  Values for 1 field has been supplied ✔


Running command speakeasy merge --schemas=[/Users/phil/src/bump/train-travel-api/openapi.yaml,/Users/phil/src/examples-examples/oas3.yaml] --out=test.yaml

Validating OpenAPI spec /Users/phil/src/bump/train-travel-api/openapi.yaml...

INFO    Using ruleset speakeasy-recommended
Lint report available to view at: https://app.speakeasy.com/org/protectearth/protectearth/linting-report/da3eeca96c5039f91a66edfc040ca975
WARN    validation warn: [line 29] oas3-host-not-example - Server URL should not point at example.com: matches the expression example\.com
Successfully validated /Users/phil/src/bump/train-travel-api/openapi.yaml
Validating OpenAPI spec /Users/phil/src/examples-examples/oas3.yaml...

INFO    Using ruleset speakeasy-recommended
Lint report available to view at: https://app.speakeasy.com/org/protectearth/protectearth/linting-report/4155c979bab17266809c505d3fa211fe
Successfully validated /Users/phil/src/examples-examples/oas3.yaml
{"time":"2025-05-12T14:12:43.498087+01:00","level":"ERROR","msg":"unable to open the rolodex file, check specification references and base path","file":"/Users/phil/src/speakeasy/developer-docs/models/todo-full.v1.json","error":"open /Users/phil/src/speakeasy/developer-docs/models/todo-full.v1.json: no such file or directory"}
{"time":"2025-05-12T14:12:43.499571+01:00","level":"ERROR","msg":"error building path item: schema build failed: reference './models/todo-full.v1.json' cannot be found at line 265, col 23"}
component ./models/todo-full.v1.json does not exist in the specification

I know merge has a different use case to bundling but if it cant pull in a ref then it should ignore it, allowing the main openapi files to be merged then point to that $ref which is hopefully still in the same folder.

Screenshots

_DOCS-5092