Adjust combat stats after playtest 1

Playtest 1 (first two pushes, ~40 min game time — pacing on target)
found the railgun_s-spam-cruiser meta and confirmed the repair tool as
overpowered (second signal after the persistent arena escort margin):

- repair_tool 9 -> 4 HP/s: the arena only prices in-fight sustain; real
  runs add free between-wave top-offs across the whole swarm
- railgun_l range 100 -> 130: now outranges stations (120), buying the
  siege role the capital ladder promises
- railgun_m 14 -> 16 dmg, range 70 -> 80: concentration tax softened so
  the ladder reads "pay some DPS efficiency for reach", not
  "strictly worse"
- new tracked arena: railgun_s-spam cruisers vs default cruisers

Module costs untouched, so all threat values stay valid. Docs updated
(derived.md, history.md playtest record, README status).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DyCu8vwChKMbLJQ3xosYEN

docs/balancing/README.md

@@ -21,8 +21,11 @@ REQ-* ids in [../requirements.md](../requirements.md).
 
 First full balancing round complete (2026-07-06): targets → tree →
 numbers → threat-calculator parity → combat stats (arena-converged) →
-pacing. Next step: full-game playtests against the run-shape targets in
-`targets.md`.
+pacing. Playtesting in progress: playtest 1 (first two pushes) found the
+railgun_s-spam-cruiser meta and confirmed repair as overpowered — combat
+stats adjusted, see `history.md`. Next: re-run the arena suite against
+the adjustments, then continue playtests against the run-shape targets
+in `targets.md`.
 
 ## Open action items