Phase 02 — A hand of dice

Build a custom hand of dice and roll all of them at once.

Added

• Top bar with a "Hand" toggle button that opens/closes the Hand pane
• Hand pane: one row per die type (enable checkbox, shape icon, minus/count/plus), plus an "Add die" popup listing all 8 types (d4/d6/d8/d10/d12/d20/d100 and a d2 coin flip) in a 2x4 grid, disabling types already in the hand
• Drop area now renders every die in the hand, each labeled with its type, instead of a single fixed d6
• Distinct 2D shape per die type (triangle, diamond, kite, pentagon, hexagon, octagon, plus the existing pip d6 and a coin) so a mixed hand is readable at a glance
• Rolling now covers the whole hand: each die animates for an independent random duration (0.5-2s) and settles on its own; the result popup shows the sum once every die has stopped

Changed

• Unchecking a die type in the hand only excludes it from rolls; its count is preserved and restored when re-enabled (previously reset to zero)
• Newly added die types start at count 1 instead of 0

See CHANGELOG.md for details.