feat: Upgrade tooltip — click-bonus and global-multiplier variants #121

Summary

Extend the upgrade tooltip system (shipped in #104 / PR #120) to cover the two upgrade types that were intentionally deferred: click-bonus upgrades and global-multiplier upgrades.

Background

PR #120 implemented delta-TD/s tooltips for generator upgrades only. The original #104 story included two additional tooltip variants that were explicitly marked out of scope for that PR and tracked here.

Acceptance criteria

• For click-bonus upgrades: tooltip shows "Click bonus: +X TD/click" reflecting the delta to click power after purchase, accounting for all current multipliers.
• For global-multiplier upgrades: tooltip shows "Multiplies all TD/s: current X.XX → new Y.YY TD/s" rather than a flat delta.
• Delta values are computed live and reflect the current multiplier stack at hover time.
• Both variants share the same visual style as the generator tooltip (dark background, monospace font, neon accent for the delta line).
• Mobile ℹ️ icon trigger works for both variants (consistent with generator tooltip behaviour).
• Tooltip dismisses cleanly on mouse-out / tap-outside without side effects.
• Unit tests cover the new delta selectors for both upgrade types.
• No regressions on existing generator tooltip behaviour.

Out of scope

• Comparison tooltips ("this vs that upgrade")
• Prestige shop upgrade tooltips (separate follow-up)

Technical notes

• Builds on the pure-selector pattern established in PR feat: upgrade tooltip shows delta TD/s preview before purchase #120.
• Click-bonus delta: (upgradeClickBase × (ownedCount + 1) × currentClickMultipliers) − currentClickPower.
• Global-multiplier delta: currentTotalTDs × (newMultiplier − 1) expressed as a before/after TD/s pair.
• Use the same Mantine <Tooltip> / <Popover> component; extend the existing tooltip component rather than creating a new one.

Definition of Done

• Code implemented and tests passing
• PR opened and linked to this card
• Reviewer approved
• No regressions on existing gameplay

-- Pam (HiveLabs PM agent)