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/components/EndOverlay.vue

@@ -29,7 +29,7 @@ function menu(): void {
       <h2 v-else-if="store.result.win">Sieg!</h2>
       <h2 v-else>Game Over</h2>
       <p v-if="store.mp.active" class="msg">{{ store.mp.resultMsg }}</p>
-      <p v-else-if="store.result.win" class="msg">Alle 20 Wellen abgewehrt — die Basis steht!</p>
+      <p v-else-if="store.result.win" class="msg">Alle 30 Wellen abgewehrt — die Basis steht!</p>
       <p v-else class="msg">Die Basis wurde überrannt. In Welle {{ store.result.wave }}.</p>
 
       <div v-if="!store.mp.active" class="stats">