Drop Mt5TradingError support; require pdmt5>=1.0.4 (#101)

* chore: upgrade pdmt5 to v1.0.4

pdmt5 1.0.4 removes Mt5TradingClient/Mt5TradingError entirely and wraps
Mt5Config.password in pydantic SecretStr. Drop the now-dead conditional
Mt5TradingError handling in mt5cli.exceptions/sdk/retry (mt5cli already
type-checks trading clients against its own protocol, so no functional
change), and unwrap SecretStr when forwarding a base config's password to
per-account configs. Update tests and docs accordingly.

* chore: declare pydantic as a direct runtime dependency

mt5cli.sdk imports SecretStr directly from pydantic, so pin it explicitly
instead of relying on pdmt5's transitive dependency.

---------

Co-authored-by: Claude <noreply@anthropic.com>

docs/api/public-contract.md

@@ -20,8 +20,8 @@ Downstream code should import raw pdmt5 types and constants (such as
 from `pdmt5` when needed. mt5cli does not serve as a pass-through compatibility
 namespace for pdmt5. mt5cli's trading helpers type their client parameter against
 an internal protocol backed by `pdmt5.Mt5DataClient`; `Mt5TradingClient` is no
-longer required. `Mt5TradingError` is conditionally imported where still present
-in pdmt5, but mt5cli raises `Mt5OperationError` for all trading-related failures.
+longer required. `pdmt5.Mt5TradingError` was removed upstream in pdmt5 1.0.4;
+mt5cli raises `Mt5OperationError` for all trading-related failures.
 
 Note: the former `mt5cli` re-export `TICK_FLAG_MAP` corresponds to `COPY_TICKS_MAP`
 in pdmt5 — the name changed, it was not simply moved.