fix(desktop): keep storyboards distinct from dashboards on shared code paths

[lauren-jacksonSFDC]

Work item: W-23854534 — bring storyboards to parity with worksheets/dashboards.

Decision

A story serializes as <dashboard type='storyboard'> and already rides the dashboard machinery (apply, cache, validation, inventory). This closes the storyboard/dashboard consistency gaps that do not need the deferred whole-workbook read fallback. The rule the codebase now keeps: the dashboard metadata resolvers treat a <dashboard type='storyboard'> as not a dashboard, so a story never leaks into the dashboard surface.

Changes

• Dashboard fallback excludes storyboards (bug fix). listDashboardRefs / resolveDashboardRef / extractDashboardXml now skip @_type='storyboard'. Before this, on an older Desktop build using the whole-workbook-document fallback, list-dashboards returned stories and get-dashboard-xml could hand back a story fragment as a dashboard.
• Kind-aware apply errors. resolveCanonicalDashboardName takes the load kind, so a storyboard apply that trips the name / workbook-document gate is told about storyboardName, not dashboard_name. The <dashboard> element tag and the read-cached-xml dashboard= selector stay literal — a story is a <dashboard> element and is sliced with that selector.
• get-storyboard-xml aligned to its get-xml siblings. storyboardName is now required, the deprecated storyboard alias param is dropped, and the description matches get-dashboard-xml / get-worksheet-xml. Shrinks the dynamic-authoring tool surface by 51 bytes (byte-budget re-pinned in server.desktop.test.ts).
• Tests. New listStoryboards.test.ts; storyboard slice/splice cases in the cache tests; dashboard-resolver exclusion cases.

Deferred (out of scope, by design)

• The whole-workbook read fallback for list-storyboards / get-storyboard-xml — only helps Desktop builds that serve /v0/workbook/document but not the newer /storyboards routes (a narrow window). Consequence: with dashboards now excluding stories, a story on such an old build is simply not enumerable there (correct, not misclassified).
• Adding list-storyboards to the default DYNAMIC_AUTHORING_TOOL_PROFILE (discovery-only; editing a named story still works).

Testing

• Touched-file unit tests green; downstream suites (read gateway, storyboard apply, compose, contract, http, emitted-references) green.
• npm run lint clean.
• npm run build:desktop succeeds.

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