fix: validate selfRegister positions and refresh market-intel quotes

[haidrrrry]

Summary

Fixes two open upstream issues:

• unsupported operand type(s) for /: 'str' and 'str' #141 — Validate selfRegister initial position quantity and entry_price with Pydantic instead of accepting raw dicts (prevents invalid/zero values and type errors).
• Market Intelligence API returns stale prices (1-2 days delayed) #188 — When Alpha Vantage intraday quotes are unavailable (demo key / missing key), fall back to yfinance for /api/market-intel/stocks/{symbol}/latest so current_price is same-day instead of 1–2 day old snapshot data. Adds price_as_of, price_stale, and price_status handling for the yfinance source.

Also normalizes short positions registered via selfRegister to negative quantity (consistent with trade signal position updates).

Related issues

Fixes #188
Related to #141, #185

Test plan

• pytest service/server/tests/test_market_intel.py — yfinance fallback
• pytest service/server/tests/test_agent_register_positions.py — validation + short qty sign
• pytest service/server/tests/test_services.py — short add weighted entry price (existing)

Notes

• Issue transactions history not right. #186 (short weighted average on add) already appears fixed upstream; left unchanged.

[haidrrrry]

Maintainer note — verification run locally:

cd service/server
ALLOW_SQLITE=true pytest tests/test_market_intel.py tests/test_agent_register_positions.py tests/test_services.py -q
# 18 passed

Scope is intentionally small (5 files). No MCP/Docker/README changes.

If you prefer yfinance fallback behind an env flag, happy to adjust in a follow-up commit.

[haidrrrry]

@TianyuFan0504 friendly ping when you have a moment — small bugfix PR for #188/#141. Happy to split or adjust scope if easier to review.