M0: skelett, byggkedja och dokumentation för JP Subway Pussel

- Go 1.27 + Ebitengine v2.10, intern upplösning 320x180 med heltalsskalning
- internal/res (resursuppslag), internal/rng (seedad slump), internal/level
  (banformat, validering, BFS-lösbarhet) med tester; internal/archtest
  kontrollerar att bara presentationslagret beror på Ebitengine
- tools/build: debug -> build/debug/, release -> build/release/<os>-<arch>/
  med resources/ bredvid binären; Windows korsbyggs utan C-verktyg
- VS Code tasks (build/test/release) och launch (dlv)
- Första banan 001-flygplatsen, sv/en-texter, skyltordbok, placeholder-sprite
- doc/: spelbeskrivning (renskriven), mål och tester, roadmap med teknikval
  (M0–M12), plan.md; README med bygg- och beroendeinformation

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

resources/data/levels/001-flygplatsen.json

@@ -0,0 +1,35 @@
+{
+  "id": "001-flygplatsen",
+  "name": { "sv": "Flygplatsen", "en": "The Airport", "ja": "空港" },
+  "difficulty": 1,
+  "destination": { "ja": "新宿", "romaji": "Shinjuku", "sv": "Shinjuku", "en": "Shinjuku" },
+  "timeLimitSec": 0,
+  "grid": [
+    "####################",
+    "#S.....#.....i.....#",
+    "#.###.##.###.#.###.#",
+    "#...#....#...#...#.#",
+    "###.######.#####.#.#",
+    "#...#....#.....#.#.#",
+    "#.###.##.#####.#.#.#",
+    "#.....#T.......#...#",
+    "#.#####.#########.##",
+    "#....GG......i..GG.#",
+    "#..p.....##......P.#",
+    "####################"
+  ],
+  "trains": [
+    {
+      "platform": "P",
+      "line": { "ja": "成田エクスプレス", "romaji": "Narita Ekusupuresu", "en": "Narita Express" },
+      "destination": { "ja": "新宿", "romaji": "Shinjuku", "en": "Shinjuku" },
+      "correct": true
+    },
+    {
+      "platform": "p",
+      "line": { "ja": "京成本線", "romaji": "Keisei Honsen", "en": "Keisei Main Line" },
+      "destination": { "ja": "京成上野", "romaji": "Keisei-Ueno", "en": "Keisei-Ueno" },
+      "correct": false
+    }
+  ]
+}