fix(editor): preserve canvas position on zoom reset

[MelmacAlpha]

Summary

Keeps the canvas work area in place when resetting the editor zoom to 100% with Cmd/Ctrl+0 or the toolbar percentage control.

• Replaces the old reset behavior that set the canvas pan to (0, 0).
• Uses the visible canvas center as the zoom origin, preserving the content under the current work area.
• Routes the toolbar reset through the canvas hook, so it uses the live transform and cancels a pending debounced gesture commit.
• Applies the same behavior to the keyboard shortcuts and toolbar control.
• Adds focused regression coverage for keyboard and toolbar resets and updates the editor documentation.

Verification

• bun run build — passes.
• bun test — 7,039 passed, 14 failed; the failures are unrelated environment issues in server-artifact path isolation and collab relay port allocation.
• bun run lint — passes.
• Focused regression tests:
  bun test src/__tests__/canvas/canvasSlice.test.ts src/__tests__/canvas/canvasMath.test.ts src/__tests__/canvas/useCanvasWheelSync.test.tsx src/__tests__/toolbar/toolbar.test.ts
• TypeScript project check: bun node_modules/typescript/bin/tsc -b --pretty false

Checklist

• Tests cover behavior changes.
• Docs were updated when behavior changed.
• No compatibility shim was added for old pre-release behavior.
• No secrets, local databases, uploads, or generated artifacts are included.

Assisted-by: OpenAI Codex

[chatgpt-codex-connector]

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