Context
-------
Every broker connector needs a uniform shape so the orchestrator can
fan out without knowing provider-specific details. Normalisation (GBP
conversion) lives outside providers on purpose — keeping providers
native-currency-emitters means we can re-normalise historical activity
when HMRC rates land without re-fetching from the broker.
This change
-----------
- providers/base.py: Provider Protocol with `accounts()` and async
`fetch(since, before)` iterator. No abstract base class — duck-typed
Protocol so each concrete provider stays independent.
- normaliser.py: takes a native Activity + FxCache, returns a copy
with amount_gbp/fx_rate_gbp/fx_rate_source filled in. Two modes:
qty*price for BUY/SELL, amount for DIVIDEND/DEPOSIT/etc.
- Namespace packages for providers/, providers/parsers/, sinks/ so
future modules slot in cleanly.
Test plan
---------
## Automated
- poetry run pytest -q → 23 passed
- poetry run mypy broker_sync tests → Success: no issues found in 14 source files
- poetry run ruff check . → All checks passed!
## Manual Verification
Not applicable at this layer.
