Chore/cleanup save trim css ux

[JLeshnick]

refactor: remove dead save-session concept and dead-code cleanup
a2e3240

• Delete SaveSlot interface (types.ts) — was never imported or used
• Remove Ctrl+S autosave-reminder handler (App.tsx) and its shortcut entry (SettingsDialog)
• Fix stale SettingsDialog copy referencing non-existent '.json saved game files'
• Correct docs (CLAUDE.md, CONTEXT.md, ARCHITECTURE.md) to remove labyrinth_saved_slots_list / named-slots claims; describe actual single-slot autosave
• Remove unused _atlasUrl param from scanBoard() (boardScanner.ts) and update call site (BoardScanModal.tsx)
• Replace undefined stone-850/stone-750 shades with valid stone-700/stone-800; drop inconsistent dark: variant prefixes (app uses [data-theme], not Tailwind dark:)

feat: UX improvements — Stats button, tablet toolbar, split timer, tu…
4f11c61
…rn-model guide

• AppHeader: lower desktop action toolbar breakpoint from lg: to md: so tablets
  (iPad, small laptops) no longer lose undo/redo/rotate/mute controls
• AppHeader: Stats is now reachable on desktop — adds a BarChart2 button in the
  game-mode toolbar wired to onToggleStats (was previously aliased unused _onToggleStats;
  the only working open path was the mobile compact panel Gauge button)
• AppHeader: split timer control out of the overloaded Play/pause/resume step-nav
  button — Play Game now only starts/ends the game; timer shows as a separate pill
  with its own pause/resume toggle and Pause/Clock icon
• AppHeader: activate showStats prop to highlight the Stats button when open
• SetupPanel: swap RotateCw → RefreshCcw for Reset Layout to disambiguate from the
  Rotate Board button in the header (RotateCw now unambiguously means board rotation)
• WelcomeGuide: add step 4 explaining the 2-phase slide→move turn model and how to
  set a custom target by tapping any board tile

feat: solver improvements — depth control, 1-move targets on by defau…
13634de
…lt, full sequence display

• Default showOneMoveTargets to true so reachable-in-one-move targets are visible
  immediately without needing to toggle them on
• Replace hardcoded SOLVER_MAX_TURNS=3 constant with state (solverDepth) initialized
  from localStorage (labyrinth_solver_depth); defaults to 3 and re-triggers the solver
  effect when changed so results update instantly
• Add solver depth selector (1–5) in SettingsDialog Experimental section, wired through
  AppHeaderProps → AppHeader → SettingsDialog; shows (default)/(faster)/(slower) hint
• Remove multi-card sequence truncation in SolverPanel: show full card order with → arrows
  instead of slicing at 3 with an ellipsis

fix: restore timer inside Game button, rename Play Game -> Game
4bcf0d3
Re-integrates the stopwatch display and pause/resume behavior back into
the step-nav button (matching the original design). Clicking the active
Game button toggles the timer; clicking when the game hasn't started
begins the game. Also renames the button label from "Play Game" to
"Game" for brevity.