Reframe screenshot views to fit model after edits

[kmatzen]

Summary

• The "current" viewport capture now computes a zoom-to-fit position from the model bounding box instead of using the raw camera position, so the model is always fully visible after parameter edits
• Saves and restores camera quaternion and orbit controls target to prevent the viewport from jumping after screenshots are captured

Test plan

• Edit a model's parameters (e.g. make a box much larger) then send a chat message — verify the captured screenshots show the full model, not a zoomed-in partial view
• After sending a message with screenshots, verify the viewport doesn't jump or change orientation
• Verify the front/right/top orthographic views still show correct framing with rulers

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