Add ability to select all nodes/edges from context menu

[Eepsita12]

Description

Adds context menu options on the graph canvas to:

• Select all nodes
• Select all edges
• Select all graph elements

The selection replaces any existing selection using replaceGraphSelection.

Validation

Tested locally using the Nobel Prize SPARQL endpoint.

Verified that:

• "Select all nodes" selects all rendered nodes
• "Select all edges" selects all rendered edges
• "Select all" selects both nodes and edges
• Existing selections are replaced correctly

Note:
pnpm checks currently fails locally due to ESLint configuration issues after recent upstream changes, and pnpm test reports existing unrelated proxy-server/Windows-specific failures.

Related Issues

Fixes #1507

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.