Parse and render stack frames in rwx lint output

[robinaugh]

Goes with rwx-cloud/language-server#30 and #370 (already merged)

Summary

• Adds StackTrace []messages.StackEntry field to CheckDiagnostic
• Parses relatedInformation from LSP diagnostic responses into stack trace entries (strips file:// prefix, converts 0-based to 1-based line/column)
• Renders stack frames in multiline output using the existing at name (file:line:col) format
• StackTrace appears in JSON output via Go's default PascalCase marshaling

Context

Depends on rwx-cloud/language-server#30, which populates relatedInformation on LSP diagnostics from the parser's stack trace arrays. Without that change, the language server never emits relatedInformation, so this CLI code has nothing to parse.

Before / After

rwx lint <file>

Before

╰─⠠⠵ rwx lint /private/tmp/test-lint/.rwx/ci.yml
/private/tmp/test-lint/.rwx/ci.yml:2:3  [error]
A base layer must have a `tag` key if it has an `os` key

/private/tmp/test-lint/.rwx/ci.yml:4:1  [error]
Unexpected property `shared`
Expected one of the following keys: `aliases`, `base`, `concurrency-pools`, `on`, `tasks`, `tool-cache`

/private/tmp/test-lint/.rwx/ci.yml:9:9  [error]
Unexpected property `badproperty`
Expected one of the following keys: `after`, `agent`, `auto-cancel`, `background-processes`, `cache`, `docker`, `env`, `env-config`, `filter`, `health-timeout`, `if`, `key`, `outputs`, `parallel`, `retry`, `run`, `terminate-grace-period-seconds`, `timeout`, `timeout-minutes`, `tool-cache`, `use`

Checked 1 file and found 3 problems.

After

╰─⠠⠵ ./rwx lint /private/tmp/test-lint/.rwx/ci.yml

/private/tmp/test-lint/.rwx/ci.yml:2:3  [error]
A base layer must have a `tag` key if it has an `os` key

/private/tmp/test-lint/.rwx/ci.yml:4:1  [error]
Unexpected property `shared`
Expected one of the following keys: `aliases`, `base`, `concurrency-pools`, `on`, `tasks`, `tool-cache`

/private/tmp/test-lint/.rwx/ci.yml:9:9  [error]
Unexpected property `badproperty`
Expected one of the following keys: `after`, `agent`, `auto-cancel`, `background-processes`, `cache`, `docker`, `env`, `env-config`, `filter`, `health-timeout`, `if`, `key`, `outputs`, `parallel`, `retry`, `run`, `terminate-grace-period-seconds`, `timeout`, `timeout-minutes`, `tool-cache`, `use`
  at /private/tmp/test-lint/.rwx/ci.yml:5:3

Checked 1 file and found 3 problems.

rwx lint <file> -o json

Before

╰─⠠⠵ rwx lint /private/tmp/test-lint/.rwx/ci.yml -o json 
{"Diagnostics":[{"Severity":"error","Message":"A base layer must have a `tag` key if it has an `os` key","FilePath":"/private/tmp/test-lint/.rwx/ci.yml","Line":2,"Column":3},{"Severity":"error","Message":"Unexpected property `shared`\nExpected one of the following keys: `aliases`, `base`, `concurrency-pools`, `on`, `tasks`, `tool-cache`","FilePath":"/private/tmp/test-lint/.rwx/ci.yml","Line":4,"Column":1},{"Severity":"error","Message":"Unexpected property `badproperty`\nExpected one of the following keys: `after`, `agent`, `auto-cancel`, `background-processes`, `cache`, `docker`, `env`, `env-config`, `filter`, `health-timeout`, `if`, `key`, `outputs`, `parallel`, `retry`, `run`, `terminate-grace-period-seconds`, `timeout`, `timeout-minutes`, `tool-cache`, `use`","FilePath":"/private/tmp/test-lint/.rwx/ci.yml","Line":9,"Column":9}],"FileCount":1,"FixedCount":0}

After

╰─⠠⠵ ./rwx lint /private/tmp/test-lint/.rwx/ci.yml -o json
{"Diagnostics":[{"Severity":"error","Message":"A base layer must have a `tag` key if it has an `os` key","FilePath":"/private/tmp/test-lint/.rwx/ci.yml","Line":2,"Column":3,"StackTrace":null},{"Severity":"error","Message":"Unexpected property `shared`\nExpected one of the following keys: `aliases`, `base`, `concurrency-pools`, `on`, `tasks`, `tool-cache`","FilePath":"/private/tmp/test-lint/.rwx/ci.yml","Line":4,"Column":1,"StackTrace":null},{"Severity":"error","Message":"Unexpected property `badproperty`\nExpected one of the following keys: `after`, `agent`, `auto-cancel`, `background-processes`, `cache`, `docker`, `env`, `env-config`, `filter`, `health-timeout`, `if`, `key`, `outputs`, `parallel`, `retry`, `run`, `terminate-grace-period-seconds`, `timeout`, `timeout-minutes`, `tool-cache`, `use`","FilePath":"/private/tmp/test-lint/.rwx/ci.yml","Line":9,"Column":9,"StackTrace":[{"file_name":"/private/tmp/test-lint/.rwx/ci.yml","line":5,"column":3,"name":""}]}],"FileCount":1,"FixedCount":0}

Test plan

• go test ./internal/... ./cmd/... passes
• golangci-lint run ./... passes
• Create a YAML file with an alias that merges invalid content, run rwx lint and verify stack frames appear in multiline output
• Run rwx lint -o json and verify StackTrace appears on diagnostics
• Run rwx lint -o oneline and verify no stack frames (by design)