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".

README.md

@@ -152,11 +152,18 @@ Türme ab Level 4 erhalten im Spiel eine pulsierende **Evolutions-Aura** (orange
 
 ## Gegner
 
+**Kampagne: 30 Wellen** (danach Endlos). Die Gegnerstärke skaliert pro Welle quadratisch — späte Wellen brauchen evolvierte Türme (Level 6+) und Forschung.
+
 - **🟢 Kriecher:** Standard-Einheit, gut für frühes Gold
 - **🟡 Läufer:** Sehr schnell – Bogentürme oder Eisturm nötig
 - **⬜ Panzer:** Zäh, kostet **2 Leben** bei Durchbruch
 - **🟣 Flieger:** Ignorieren den Weg und fliegen auf halber Höhe geradeaus (nur Bogenturm, Eisturm, Tesla, Laser!)
-- **🔴 Boss:** Riesige Lebensleiste, kostet **5 Leben** (Wellen 10, 15, 20 …)
+- **🔴 Boss:** Riesige Lebensleiste, kostet **5 Leben** (Wellen 10, 15, 20, 25, 30)
+- **🟤 Brute** *(ab Welle 8):* Schneller Panzer — zäh UND flott, kostet 2 Leben
+- **⚪ Phantom** *(ab Welle 12):* Schneller Flieger mit viel Leben — Luftverteidigung Pflicht
+- **🦂 Skorpion** *(ab Welle 14):* Extrem schnell am Boden, kostet 2 Leben
+- **🗿 Golem** *(ab Welle 18):* Laufender Bunker, riesige Lebensleiste, kostet 3 Leben
+- **🐲 Drache** *(ab Welle 22):* Fliegender Boss, kostet 3 Leben — eigene Boss-Leiste am oberen Rand
 
 ---