Labeled toolbar pill, plan-aware default model, click-to-rename, fix re-upload no-op

[aperson30]

Summary

• The floating "show toolbar" gear was a bare, unlabeled icon floating alone in the top-right corner - turned it into a labeled pill (icon + "Show toolbar" text) so it reads as an actual control.
• Model picker defaults to a model the signed-in account can actually run (ePAI if the plan includes it, LesionSegmenter otherwise - Free only gets LesionSegmenter) instead of "None". Picked in an effect once the account's plan is known, guarded so it never overwrites a choice the user already made and never fires for a signed-out visitor.
• Completed-scan rename: click the scan's name directly to edit it (underline on hover is the only affordance), no separate pencil-icon button - matches how Claude's own conversation titles work.
• Real bug fix: re-selecting a file you'd already picked once (e.g. clicking "Select NIfTI file" again after Run clears the dropzone back to empty, and picking the SAME file) silently did nothing - all the UI steps worked, but nothing uploaded. Root cause: a native <input type="file"> doesn't fire a change event if its value is set to the same path twice in a row, and the handler never reset the input after a successful pick. Fixed by resetting it, matching the pattern the DICOM folder picker already used.

Test plan

• npm run build - clean
• vitest run - 298/298 passing (updated planGating.test.tsx and uploadScheduling.test.tsx for the new plan-aware default)
• Manual: pick a NIfTI file, run it, then pick the exact same file again - confirm it uploads a second time
• Manual: open the viewer, hide the toolbar, confirm the "Show toolbar" pill is clear and doesn't overlap anything
• Manual: as a free-plan user, confirm the picker defaults to LesionSegmenter (not a locked model)