Apply reviewer audit findings on the tooltip system

Details

8 confirmed findings from the 4-lens reviewer panel (coverage / copy /
positioning / a11y), with majority survival through the 3-verifier
adversarial pass:
- Add `data-tip-pos="bottom-right"` variant: right-anchored tip for
  controls flush with the viewport edge. Used on the v2/v1 version chips
  (a centered tip on v1 clipped off-screen) and the mobile hamburger.
- Hamburger toggle (#v3-nav-toggle): icon-only — add `data-tip="Open menu"`
  for sighted keyboard users tabbing in at narrow widths.
- Theme toggle tip: "Light / dark" → "Toggle theme" (slash read as a status
  label, not the imperative action the control performs).
- Copy-email tip: "Copies jkrichel@syr.edu" → "Copy jkrichel@syr.edu"
  matching the imperative voice of the visible "Copy email" label.
- Copy-email button gains an explicit `aria-label` with the address so
  screen-reader users hear the email they're about to copy (the visible
  label only says "Copy email").

Files changed (4)