feat(balance): 30-wave campaign, 5 new enemy types, steeper per-wave scaling

The campaign was too easy: a handful of un-upgraded towers stopped
everything. This makes the game substantially harder across three axes.

Campaign extended from 20 to 30 hand-tuned waves (endless now starts at
31). Victory messages, HUD label (via store.totalWaves synced from
TOTAL_WAVES), start screen, lobby and README updated.

Five new enemy types debut in later waves, each with a hand-drawn
canvas look:
- Brute (wave 8): fast tank hybrid, 130 HP, 2 lives
- Phantom (wave 12): fast flyer with real HP, 2 lives
- Scorpion (wave 14): very fast ground, 2 lives
- Golem (wave 18): walking bunker, 560 HP, 3 lives
- Dragon (wave 22): flying boss, 950 HP, 3 lives, gets its own top
  boss health bar like the boss

Per-wave HP scaling steepened (1 + 0.16m + 0.025m², was 0.18m + 0.02m²):
wave 10 now ~4.6x (was 4.2x), wave 20 ~13.2x (was 11.6x), wave 30 ~29x.
Late waves mix the new types into heavy compositions; wave 30 is the
final wall (3 bosses, 2 dragons, 4 golems, 12 scorpions). Endless waves
scale all ten types with bosses every 5 and dragons from endless+2.

Balance validated with the headless greedy-bot simulation: the bot
(capped around tower level 5 on fixed spots) previously trivially won
the campaign and now dies at wave 29 — clearing wave 30 requires
evolved towers (level 6+), research bonuses and good placement. The
sim docs were updated to describe this new tuning philosophy.

New render smoke test (npm test): draws all ten enemy kinds through
the real renderer with a stub 2D context, two frames each with slow/
DoT/flash effects active, guarding every drawEnemy code path. 55 checks
green, build clean. Browser-verified: campaign starts and HUD shows
"Welle x/30".

src/game/mpgame.ts

@@ -342,7 +342,7 @@ class MpGameController {
     if (this.ended) return
     if (this.mode === 'coop') {
       if (engine.phase === 'gameover') this.endGame(false, 'Eure Basis ist gefallen…')
-      else if (engine.phase === 'victory') this.endGame(true, 'Alle 20 Wellen gemeinsam geschafft!')
+      else if (engine.phase === 'victory') this.endGame(true, 'Alle 30 Wellen gemeinsam geschafft!')
       return
     }
     const mine = this.engines[this.myId]