Combat stats round 2 from arena round 1 findings

Round 1 findings: concentrated fleets won all four equal-threat
cross-tier matchups flawlessly; glass destroyers beat armored; repair
escort beat raw numbers flawlessly; two stations annihilated a 3x
threat swarm through 200 m approach fire; team 1 won all three mirror
matches (possible sim bias, recorded as action item 6, plus action
item 7 for HP-margin logging).

Knob changes, deliberately few for clean attribution: concentration
tax on m/l gun DPS (railgun_m damage 17 -> 14, railgun_l 70 -> 52),
armor_plates 640 -> 1000 HP (~31 HP/threat: killing removes enemy DPS
while surviving merely delays, so HP must be cheaper than DPS), repair
25 -> 12 HP per cycle (~1 HP/s per threat: in-combat sustain removes
enemy DPS and must be priced like DPS), station range 200 -> 120. Gun
ranges untouched; if concentration still wins flawlessly in round 2,
the range ladder is the next suspect. Anchors and findings documented
in content_design.md; fitted threat values are unaffected by stat
changes, so the arena suite counts stay valid.

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

docs/progression_design.md

@@ -373,3 +373,15 @@ in `requirements.md` and the git history). Still open:
    one matching deposit tile). Touches REQ-BLD-MINER ("every asteroid
    tile is equivalent" no longer holds), REQ-GW-ASTEROID-EXPAND /
    REQ-EXP-*, `world.toml`, and `visuals.toml`.
+6. **Investigate team-1 bias in balancing arenas.** In arena round 1
+   (July 2026), team 1 won all three mirror matches with large margins
+   (8/20, 3/6, 1/2 survivors). Re-run mirrors repeatedly; if team 1
+   wins consistently, find and fix the asymmetry (spawn geometry, tick
+   processing order, target-selection tie-breaking). Mirror matches
+   must be statistically symmetric or every arena result carries a
+   side-dependent error.
+7. **Log remaining HP in the balancing arena results.** Win/loss alone
+   hides the margin ("1/1 battleship" can mean 95% or 5% HP left). Add
+   the surviving entities' remaining HP fraction (or a per-team total
+   EHP percentage) to the arena end state, so equal-threat matchups can
+   be tuned toward near-draws quantitatively.