Add durable deterministic shadow execution

[howdymary]

What changed

• adds immutable fixed-point shadow contracts, UTC replay/system clocks, and a credential-free validated-capture feed
• adds deterministic displayed-depth and later-trade fills without RNG or fabricated liquidity
• adds signed, reservation-aware risk with reduce-only splitting and conservative exposure accounting
• adds a SQLite v1 WAL/FULL/FK state journal with fenced writer leases, deterministic IDs, durable decisions/intents/orders/fills/positions, breakers, cancel-all, reconciliation, and canonical state hashes
• adds atomic per-trade allocation plans so crash/replay cannot reuse queue or trade volume
• routes Packet 4 typed providers through strategy.build_orders and Packet 5 replay without exposing outcomes or authenticated venue capabilities
• adds autopredict shadow run/status/cancel-all/reset, a thin autopredict-paper compatibility wrapper, strict config allowlists, example config, and operating documentation
• handles stale/gapped/reconnected feeds, conflicting duplicates, provider errors, accounting faults, daily loss, restart, and failed admin cleanup fail-closed

Why / root cause

The previous paper runner only slept and logged empty metrics. State, positions, fills, and resting orders were memory-backed, risk was not direction-aware, and there was no restart reconciliation or point-in-time replay parity. That made the required safety gate before any live consideration nonfunctional.

User and developer impact

Users can now replay validated public captures through the actual forecast→strategy→risk→fill path, persist deterministic state, inspect/cancel/reset it, and resume after crashes without duplicate provider calls or fills. Live order submission remains disabled.

Schema and migration

Introduces autopredict.shadow SQLite schema v1 and autopredict.shadow.config.v1. Shadow configuration is a strict allowlist and rejects credentials, environment substitution, live/adapter/network fields, and unknown keys. Existing paper entrypoint delegates to the new shadow runner.

Verification

• independent core reviewer: APPROVED after multiple remediation rounds
• independent integration/safety tester: APPROVED
• focused shadow suite: 31 passed before main integration
• full suite on current main stack: 453 passed
• Python 3.9 installed-wheel entrypoint/import checks: passed
• Black 26.5.1, compileall, scoped mypy, and git diff --check: passed
• sdist/wheel build and clean installed-wheel import audit: passed
• repeat/restart/fresh replay state hashes: identical
• injected crash tests prove atomic two-order trade allocation and daily-loss breaker recovery
• no authenticated request, live order, or production credential was used

Residual risks

• v1 supports persisted, validated Packet 5 capture replay; direct public polling remains intentionally unsupported until it can pass through the same immutable validation boundary
• deterministic queue-ahead is a conservative simulation assumption, not venue truth
• multi-day operational evidence has not yet been collected, so this PR does not make live execution ready

Tracks #2
Closes #7