feat(oneshot): add Anti-Flip 5m microstructure execution engine

Introduces a complete, event-driven execution engine for 5-minute
Polymarket UP/DOWN markets, implementing the Anti-Flip strategy spec.

Architecture
────────────
• EventBus          — central pub/sub bus connecting all services
• MarketFeedService — discovers 5m/15m markets via Gamma API, polls
                      CLOB orderbooks every 200–500ms, emits snapshots
• FeatureEngine     — maintains a 15s rolling buffer per market and
                      computes midSlope6s, retrace3s, imbalance, spread,
                      depthTop3 for both UP and DOWN sides
• SignalEngine      — hard gate checks (TTE, spread, depth, stale) then
                      weighted score (imbalance 35%, slope 35%,
                      spread 20%, retrace 10%) + trend confirmation
• ExecutionEngine   — limit-marketable FOK buy, market-sell FOK exit,
                      GTC limit-sell for TP; dry-run short-circuits
• RiskEngine        — consecutive loss cooldown, daily USDC loss cap,
                      session halt; all via explicit canTrade() gate
• PositionEngine    — per-market position state, TP/adverse/slope/time
                      exit evaluation on every snapshot tick
• StateMachine      — explicit state graph with guarded transitions:
                      IDLE → SETUP_READY → ORDER_PENDING → POSITION_OPEN
                      → REDUCE_ONLY → IDLE | COOLDOWN | HALTED
• Telemetry         — structured JSONL logger (data/oneshot_telemetry.jsonl)
                      recording decisions, orders, exits, and transitions

Runtime sequence (per market, per tick)
────────────────────────────────────────
A  Ingest snapshot (MarketFeedService)
B  Build features — rolling slope, retrace, imbalance (FeatureEngine)
C  Hard gate check — TTE [25,120]s, spread ≤ 0.02, depth ≥ minTopSize
D  Score + trend confirm → emit ENTER_LONG / ENTER_SHORT / NO_TRADE
E  Submit FOK limit-marketable at bestAsk
F  Fill handling — full fill / partial (reduce if TTE ≤ 25s) / timeout
G  Position management — TP, adverse (2-tick), slope drop (4s), time exits
H  Risk enforcement — P&L accounting, cooldown, daily halt

New scripts
───────────
  npm run oneshot      — live trading  (DRY_RUN=false)
  npm run oneshot-sim  — simulation    (DRY_RUN=true)
  npm run oneshot-dev  — sim + nodemon

New .env variables
──────────────────
  ONESHOT_ASSETS, ONESHOT_DURATION, ONESHOT_POLL_INTERVAL_MS,
  ONESHOT_BASE_RISK_USDC, ONESHOT_TP_TICKS, ONESHOT_SCORE_THRESHOLD,
  ONESHOT_MIN_TOP_SIZE, ONESHOT_MAX_CONSEC_LOSSES,
  ONESHOT_COOLDOWN_ROUNDS, ONESHOT_DAILY_LOSS_CAP, ONESHOT_FILL_TIMEOUT_MS

Co-Authored-By: direkturcrypto <direkturcrypto.x@mail3.me>

.env.example

@@ -124,3 +124,45 @@ SNIPER_PRICE=0.01
 # Shares per side — minimum Polymarket order size is 5 shares
 # At $0.01/share: 5 shares = $0.05 per side, $0.10 per market
 SNIPER_SHARES=5
+
+# ─────────────────────────────────────────────
+# ONESHOT ENGINE (oneshot.js / npm run oneshot-sim)
+# Anti-Flip 5m microstructure execution engine.
+# Evaluates book features on every tick and enters only when
+# momentum, depth, and spread conditions align.
+# ALWAYS test with DRY_RUN=true before going live.
+# ─────────────────────────────────────────────
+
+# Comma-separated assets to monitor (e.g. btc,eth,sol)
+ONESHOT_ASSETS=btc
+
+# Market duration: "5m" (5-minute) or "15m" (15-minute)
+ONESHOT_DURATION=5m
+
+# Book poll interval in milliseconds (200–500ms recommended)
+ONESHOT_POLL_INTERVAL_MS=300
+
+# USDC risk per trade — size = floor(ONESHOT_BASE_RISK_USDC / entryPrice), min 5 shares
+ONESHOT_BASE_RISK_USDC=5
+
+# Take-profit in ticks above entry price (1 tick = tickSize, e.g. 0.01)
+ONESHOT_TP_TICKS=1
+
+# Minimum composite score to trigger entry (0–1, higher = more selective)
+ONESHOT_SCORE_THRESHOLD=0.60
+
+# Minimum shares at the best bid AND best ask for the depth hard gate
+ONESHOT_MIN_TOP_SIZE=10
+
+# ── Risk settings ──────────────────────────────────────────────────────
+# Number of consecutive losses before entering cooldown
+ONESHOT_MAX_CONSEC_LOSSES=2
+
+# Number of market slots to skip during cooldown
+ONESHOT_COOLDOWN_ROUNDS=3
+
+# Maximum cumulative daily loss in USDC before halting all trading
+ONESHOT_DAILY_LOSS_CAP=20
+
+# Maximum milliseconds to wait for a FOK fill ack (timeout → cancel → IDLE)
+ONESHOT_FILL_TIMEOUT_MS=800