Persist DM screen splitter sizes across reloads

[HarmlessHarm]

Summary

• Save the campaign DM screen's wide-layout splitter sizes (outer left/mid/right + the two inner vertical splits) to localStorage on drag release and restore them on reload, preserving DMs' preferred layout between sessions.
• Sizes are stored as percentages so they remain layout-relative across screen resolutions.
• Override the async hk-pane registration with a sync local import in RunCampaign.vue so all Splitpanes children mount synchronously — async children caused splitpanes' equalize-on-add cascade to overwrite saved sizes with redistributed defaults on every reload.
• Drag-flag guard skips saves on resized events that don't originate from a real user drag (defends against the campaign.private toggle adding/removing the Share pane and triggering a runtime equalize).

Test plan

• Open a campaign at viewport width >= lg; drag each of the 5 splitters, reload, confirm sizes are restored
• Resize browser window to a different width and reload; confirm proportions (not pixels) are preserved
• Toggle the campaign's privacy while on the DM screen; confirm left-top doesn't get overwritten with an equalized value
• In DevTools, set localStorage["dm-screen-panes-v1"] to invalid JSON / out-of-range value / unknown key; reload and confirm graceful fallback to defaults
• Confirm mobile (narrow viewport) and legacy_campaign_layout enabled both still render with their existing hardcoded sizes and write nothing to storage

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud