Pacing pass: unlock ladder, threat rate, economy values

Replace the everything-at--1 test setup with the real progression:
starting set is exactly drone/frigate/railgun_s/salvager; the ladder
runs destroyer+repair+armor at level 0, supports at 1, the quartz gate
(cruiser, railgun_m, afterburner, chip/hardened shortcuts) at 2,
battlecruiser at 4, battleship+railgun_l at 6, dreadnought at 8,
carrier+drone_hangar at 9, with unlock_requires edges cruiser ->
battlecruiser -> battleship -> dreadnought/carrier and railgun_m ->
railgun_l.

world.toml: threat_rate_formula 2*x + 0.15*x*x (below the player's
achievable military output early, crossing at the late boundary,
overwhelming by cycle ~24), starting_building_blocks 1000 -> 200,
expansion cost 200 -> 400 flat (placeholder until action item 4),
artifact_win_count 3 -> 5 (winning means choosing the artifact over a
schematic five times across ~7 cumulative offers).

Bug fix found during the pass: the building_block recipe carried no
unlock_at_station_level, and since building blocks appear in no
schematic's materials, implicit unlocking could never reach it - the
recipe was silently locked at game start. Now explicitly -1.

All values and derivations documented in content_design.md, "Pacing
pass - first values".

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

bin/app/data/config/recipes.toml

@@ -142,8 +142,11 @@ duration_seconds = 1.5
 
 # Depth-3 chain (ore -> ingot -> plate -> block) is the factory's
 # doubling-time knob; see the block economy rules in progression_design.md.
+# Explicitly unlocked at start (-1): building blocks appear in no
+# schematic's materials, so implicit unlocking can never reach this recipe.
 [[recipe]]
 id = "building_block"
+unlock_at_station_level = -1
 building = "assembler"
 inputs = [{item = "steel_plate", amount = 2}]
 outputs = [{item = "building_block", amount = 4}]