Publish a project to the GraphForge Hub with native data and selected previews

[DecisionNerd]

Objective

Publish a project to the GraphForge Hub from VS Code by invoking Core's gf publish, following GraphForge ADR 0054 (CurateLabs/graphforge#1779) and ADR-0005.

Requirements

• Publish native GraphForge data plus explicitly selected visualization previews. Each preview is the PNG and SVG pair from XYG's static export (Define the local GraphForge intent document and the PNG/SVG export pair xyg#935), sent through Core's closed preview channel (feat(io): keep packages native-only and publish visualization previews through a closed PNG/SVG channel graphforge#1768). Nothing is selected by default.
• Never publish notebooks, apps, XYG intent documents, or saved result snapshots. Saved queries are publishable only if Core defines a native object for them.
• Core owns the credential. The extension stores no Hub tokens. Surfacing the login through vscode.authentication is an open question.
• Agent-callable, with confirm: true required, like applyProjectMutation.
• The published Version records its producing Core version (feat(io): declare the producing Core version and refuse other versions before v1 graphforge#1769). Show it in the confirmation.

Relationships

Blocked by CurateLabs/graphforge#1768, CurateLabs/graphforge#1769, CurateLabs/graphforge#1749 (gf publish), and authenticated publishing on the Hub.