docs(kanvas): document share-access fix and share/visibility notifications

[Copilot]

Sharing a design or view could report success while grants were not applied (fixed in @sistent/sistent 0.22.0). Kanvas also now surfaces three share/visibility failures that used to fail silently—none of that was documented.

Sharing Designs

• Warn owners to re-check People with Access on anything shared while the silent grant failure was live
• Note that the fix reaches Kanvas when the host UI supplies sistent 0.22.0
• Treat People with Access as the source of truth after grant/revoke

Share and visibility notifications

Document the three cases and what to do:

Situation	Notification
Visibility mutation unsupported for the resource kind	Unsupported (not success)
Share while design/view body loading or failed	Sharing unavailable
Access list fetch failed	Access list failed to load (not an empty collaborator list)

Views

• Point Operator view sharing at the designs sharing page for the same fix and notification guidance

• Fixes Document the Kanvas share fix (sistent 0.22.0) and three new share/visibility notifications #1194

[github-actions]

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[leecalcote]

Refactor this to be user-facing. No user cares about Sistent or a specific version.

[Copilot]

Refactor this to be user-facing. No user cares about Sistent or a specific version.

Updated the share-access guidance to user-facing language and removed Sistent/version references in 55272fc.