Add Space-key coverage for focused button and contenteditable controls

[coderabbitai]

Summary

Add browser-test coverage for focused buttons and contenteditable elements during
Space-key input while a Vue node drag is active.

Rationale

forwardSpaceKeyEvent in src/components/graph/GraphCanvas.vue has dedicated
exclusions for HTMLButtonElement and HTMLElement.isContentEditable.
The current tests cover text inputs and native selects, but they do not execute
these two exclusions.

Affected areas

• browser_tests/tests/vueNodes/interactions/canvas/pan.spec.ts
• src/components/graph/GraphCanvas.vue (forwardSpaceKeyEvent behavior)

Required changes

Add focused-control tests near the existing Space-key panning tests. Each test
must hold Space while the relevant control has focus and verify that canvas
panning does not start.

Cover these controls:

1. A focused native button.
2. A focused contenteditable element.

Acceptance criteria

• The button test verifies that canvasOps.isReadOnly() remains false while
  Space is held.
• The contenteditable test verifies that canvasOps.isReadOnly() remains
  false while Space is held.
• The tests use the browser-test conventions for this repository.
• The tests do not use any or as any.

Backlinks

• Pull request: Support space bar pan while dragging vue nodes #12943
• Review comment: Support space bar pan while dragging vue nodes #12943 (comment)
• Requested by: @DrJKL

[coderabbitai]

🔗 Related PRs

#12943 - Support space bar pan while dragging vue nodes [open]
#14585 - security: replace website v-html with safe rich text [open]
#15002 - test: add failing e2e repro for FE-1539 subgraph unpack boundary links [open]
#15012 - fix: re-check tab fallback after deferred error scans [open]
#15059 - test: ledger the WAS vue-height flip and the MathExpression sweep crash [merged]

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