fix(visualise): improve canvas navigation and initial view

[melkamzeranteneh]

Summary
This PR improves the usability of the MeTTaGrapher webview by enhancing interaction and resolving a packaging
configuration issue.

• Canvas Navigation: Added drag-to-pan functionality. Dragging now only initiates on the canvas background,
  preserving existing node-interaction behavior.
• Initial View: Added an automatic fitView() call on initial load to ensure graphs are properly centered and
  visible regardless of code length.
• Packaging: Added node_modules/metta-ts-typescript-plugin to .vscodeignore to resolve VSIX packaging/compilation
  issues.

Implementation Checkpoint

• Initial graph framing: fitView() now triggered automatically on load.
• Drag-to-pan navigation: Implemented (background-click only).
• Packaging fix: Updated .vscodeignore.

[MesTTo]

this requires a metta ts fix, which ill be working on. and also running npm run package die with error: not a file: node_modules/metta-ts-typescript -plugin , and also the file:./typescript-plugin dependency itself, because npm documented default is install-links=false you make the symlink and vsce fails.. now with it true, it would copy it at install time, but taht would stil lead to module not found. anyways thank you for flagging this