feat: overhaul mana conversion system to unified regen-deduction model

- New files: element-distance.ts, conversion-costs.ts, conversion-rates.ts
- All conversion types (discipline, attunement, pact) use unified formula
- Conversion costs scale exponentially by element tier (10^(d+1) raw, 10*(d+1) per component)
- Costs deducted from regen, not from mana pool
- Auto-pause on insufficient regen with UI warning
- Meditation boosts conversion rates (reduced by distance)
- Attunement levels provide +50% multiplicative bonus per level
- Guardian pacts provide +0.15/hr base rate + invoker level bonus
- Removed convertMana, processConvertAction, craftComposite from manaStore
- Stats tab shows per-element conversion breakdown with formulas
- ManaDisplay shows per-element net regen rates
- All 916 tests pass, all files under 400 lines

src/lib/game/data/conversion-costs.ts

@@ -0,0 +1,118 @@
+// ─── Conversion Cost Ratios ───────────────────────────────────────────────────
+// All conversions produce 1 unit of destination mana.
+// Costs are deducted from regen (not from the mana pool).
+//
+// For a destination element at distance d:
+//   rawCost       = 10^(d+1)
+//   componentCost = 10 * (d+1) per component
+
+import type { ElementRecipe } from '../types';
+
+export interface ConversionCost {
+  /** Destination element ID */
+  element: string;
+  /** Distance from raw mana */
+  distance: number;
+  /** Raw mana cost per 1 unit of destination */
+  rawCost: number;
+  /** Component costs: element ID → amount per 1 unit of destination */
+  componentCosts: Record<string, number>;
+}
+
+function computeRawCost(distance: number): number {
+  return Math.pow(10, distance + 1);
+}
+
+function computeComponentCost(distance: number): number {
+  return 10 * (distance + 1);
+}
+
+/** Build a ConversionCost for a base element (distance 1, no components) */
+function baseElementCost(element: string): ConversionCost {
+  return {
+    element,
+    distance: 1,
+    rawCost: computeRawCost(1), // 100
+    componentCosts: {},
+  };
+}
+
+/** Build a ConversionCost for a composite element (distance 2) */
+function compositeElementCost(element: string, components: string[]): ConversionCost {
+  return {
+    element,
+    distance: 2,
+    rawCost: computeRawCost(2), // 1,000
+    componentCosts: Object.fromEntries(
+      components.map(c => [c, computeComponentCost(2)]), // 30 each
+    ),
+  };
+}
+
+/** Build a ConversionCost for an exotic element (distance 3) */
+function exoticElementCost(element: string, components: string[]): ConversionCost {
+  return {
+    element,
+    distance: 3,
+    rawCost: computeRawCost(3), // 10,000
+    componentCosts: Object.fromEntries(
+      components.map(c => [c, computeComponentCost(3)]), // 40 each
+    ),
+  };
+}
+
+/** Build a ConversionCost for time (distance 4) */
+function timeElementCost(element: string, components: string[]): ConversionCost {
+  return {
+    element,
+    distance: 4,
+    rawCost: computeRawCost(4), // 100,000
+    componentCosts: Object.fromEntries(
+      components.map(c => [c, computeComponentCost(4)]), // 50 each
+    ),
+  };
+}
+
+// ─── Full Cost Table ──────────────────────────────────────────────────────────
+
+export const CONVERSION_COSTS: Record<string, ConversionCost> = {
+  // Base (distance 1)
+  fire: baseElementCost('fire'),
+  water: baseElementCost('water'),
+  air: baseElementCost('air'),
+  earth: baseElementCost('earth'),
+  light: baseElementCost('light'),
+  dark: baseElementCost('dark'),
+  death: baseElementCost('death'),
+  // Utility (distance 1)
+  transference: baseElementCost('transference'),
+  // Composite (distance 2)
+  metal: compositeElementCost('metal', ['fire', 'earth']),
+  sand: compositeElementCost('sand', ['earth', 'water']),
+  lightning: compositeElementCost('lightning', ['fire', 'air']),
+  frost: compositeElementCost('frost', ['air', 'water']),
+  blackflame: compositeElementCost('blackflame', ['dark', 'fire']),
+  radiantflames: compositeElementCost('radiantflames', ['light', 'fire']),
+  miasma: compositeElementCost('miasma', ['air', 'death']),
+  shadowglass: compositeElementCost('shadowglass', ['earth', 'dark']),
+  // Exotic (distance 3)
+  crystal: exoticElementCost('crystal', ['sand', 'light']),
+  stellar: exoticElementCost('stellar', ['plasma', 'light']),
+  void: exoticElementCost('void', ['dark', 'death']),
+  soul: exoticElementCost('soul', ['light', 'dark', 'transference']),
+  plasma: exoticElementCost('plasma', ['lightning', 'fire', 'transference']),
+  // Time (distance 4)
+  time: timeElementCost('time', ['soul', 'sand', 'transference']),
+};
+
+/** Get the conversion cost for an element. Returns null if not found. */
+export function getConversionCost(element: string): ConversionCost | null {
+  return CONVERSION_COSTS[element] ?? null;
+}
+
+/** Get all source types (raw + components) for a conversion */
+export function getConversionSources(element: string): string[] {
+  const cost = CONVERSION_COSTS[element];
+  if (!cost) return [];
+  return ['raw', ...Object.keys(cost.componentCosts)];
+}