fix: rebalance rawCost and componentCost formulas to be achievable with realistic regen

- Changed rawCost from exponential 10^(d+1) to linear 2*distance
  - Base (d=1): 100 → 2
  - Composite (d=2): 1,000 → 4
  - Exotic (d=3): 10,000 → 6
  - Time (d=4): 100,000 → 8

- Changed componentCost from 10*(d+1) to 3*distance
  - Composite (d=2): 30 → 6 per component
  - Exotic (d=3): 40 → 9 per component
  - Time (d=4): 50 → 12 per component

- Updated test comments and expectations in conversion-pause-bug-regression.test.ts
  and mana-conversion-component-deduction.test.ts to match new values

Root cause: The exponential rawCost formula produced values 100-10000x too high,
making mana conversion permanently paused since drain (rate × cost) always exceeded
even late-game raw regen (~20-50/hr). The new linear formula allows conversions to
be sustainable at all game stages.

Fixes #378

docs/dependency-graph.json

@@ -1,6 +1,6 @@
 {
   "_meta": {
-    "generated": "2026-06-12T08:05:43.098Z",
+    "generated": "2026-06-12T10:15:01.393Z",
     "description": "Import dependency graph for src/lib/game. Keys are files, values are arrays of files they import.",
     "usage": "To find what a file affects, search for its path in the VALUES. To find what a file depends on, look at its KEY entry."
   },