feat(pacing): soft floor-readiness guidance — answer "how much Tetris?"

[FiddlyDigital]

Players had no signal for how long to build a floor before descending. Add
advisory (never gating) guidance that scales with depth.

• Each non-boss floor has a readiness target: baseTarget + (level-1)*perLevel
  blocks (all knobs in balance.json's new floorReadiness block). Later floors
  ask for more Tetris, so play naturally lengthens as the run deepens.

• The HUD floor dial leads with readiness: "building 6/15" → a glowing "ripe"
  once the floor is built out → "linger" past target*lingerMult. One-time
  toasts fire at ripe ("descend when you are ready") and lingering ("the rift
  grows restless").

• Descent stays entirely player-driven — the stairs are never locked.

• Each descent banks a pieces/target pacing sample (non-boss floors only,
  stack-collapses count as staying to the limit). The seanchai in the mound
  reads the run's average and comments: leaving too soon, lingering too long,
  or judging it well (seanchaiEarlyRatio / seanchaiLateRatio).

• balance.json + schema + balance.ts: floorReadiness block

• types.ts: UIState.floorProgress.readiness

• game.ts: readiness target/ceiling, ripe/linger detection, dial state,
  recordFloorPacing on both descent paths, pacingAdvice, per-floor reset

• ui.ts + style.css: readiness dial segment (build/ripe/linger)

• npcEncounters.ts: seanchai pacing line in the "your tale" recount

• tests: target scaling, dial states, gating, ripe toast once, pacing tally,
  seanchai verdict bands

• README: new "Floor readiness" system row

Pacing state (pacingRatioSum/Samples) round-trips through save/resume via the
generic scalar sweep. Verified live: the dial renders building/ripe/lingering
with no page errors.

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01V6kP5vUAcNbxLK5EnPKAhv