chore(compat): enforce shared tolerance and warmup policy

[TDamiao]

Summary

• add a single compatibility policy source in scripts/compat-policy.json
• move per-indicator tolerance and burn-in config out of scripts into that shared policy
• make JS and Python comparators consume the same policy
• include policy snapshot in generated compat vectors metadata for reproducibility
• document indicator-level policy and warmup/alignment rules in README
• improve TA-Lib missing dependency error messaging in Python compat script

Validation

• npm.cmd run test:compat:technicalindicators (PASS)
• npm.cmd run test:compat:python -> explicit dependency failure on local env:
  • TA-Lib unavailable: No module named 'talib'
  • install requirements: pip install -r scripts/requirements-compat.txt

Notes

• This PR is stacked on top of feat(stateful): add streaming SMA/EMA APIs with parity and reset coverage #10 to keep review scope incremental.
• Blocking references remain TA-Lib and technicalindicators; pandas-ta remains telemetry/non-blocking.

Refs #3