feat: validate embed set state params upfront with setValidState

[AdityaHegde]

Adding setValidState({ state, failOnError }) to our embed state API.

1. Validates the state against the dashboard's metrics view and explore specs before applying it.
2. Invalid parameters are reported back, and the applied URL is canonicalized the same way it would be if the user navigated there directly.
3. The applied state is returned in appliedState

Closes APP-918

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[nishantmonu51]

@codex: review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Default to failing when validation errors are present

When callers omit failOnError, this defaults to applying the cleaned URL even if validation reported errors, but both the inline API contract above and the new public docs say the default is to fail and not apply invalid state. In that common omitted-flag case, an embedder can receive success: true and have invalid parameters silently dropped instead of the state remaining unchanged as documented.

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[chatgpt-codex-connector]

Avoid applying default-stripped URLs through session restore

Applying the canonical URL here can render a different state than the appliedState returned when the validated URL is empty or view-only and the viewer has prior embed session state. The explore embed uses DashboardStateManager with session storage enabled, and DashboardStateDataLoader.getMergedExploreState calls getPartialExploreStateFromSessionStorage for empty URLs / view-only URLs, so after a parent calls setValidState({ state: "" }) to reset the dashboard, the subsequent navigation can restore the previous session filter instead of the rill defaults that buildValidatedExploreUrl computed.

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