feat: stable MT5Client public API and infrastructure layer (#30)

* feat: add stable MT5Client public API and infrastructure layer

Introduce a reusable public API for downstream trading applications:

- MT5Client as the primary client abstraction with order_check/order_send
- schemas module with DataKind contracts, validation, and normalization
- converters, exceptions, retry, and storage facade modules
- CLI order commands now route through MT5Client
- connected_client made public; retry logic centralized
- Contract tests for API surface, schemas, and storage round-trips
- README and docs updated with Python API usage examples

Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

* fix: correct time coercion, broker-safe symbols, and execution docs

- Normalize MT5 time columns with correct second/millisecond units
- Coerce all present known MT5 time fields, including optional order times
- Preserve broker symbol casing in normalize_symbol()
- Document order_send() as a live execution primitive with clear scope boundaries
- Add contract tests for timestamp and symbol normalization behavior

Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

mkdocs.yml

@@ -1,5 +1,5 @@
 site_name: mt5cli API Documentation
-site_description: Command-line tool for MetaTrader 5
+site_description: Generic MT5 data and execution infrastructure for Python
 site_author: dceoy
 site_url: https://github.com/dceoy/mt5cli
 
@@ -56,6 +56,11 @@ nav:
   - Home: index.md
   - API Reference:
       - Overview: api/index.md
+      - Client: api/client.md
+      - Schemas: api/schemas.md
+      - Storage: api/storage.md
+      - Converters: api/converters.md
+      - Exceptions: api/exceptions.md
       - CLI: api/cli.md
       - SDK: api/sdk.md
       - Trading: api/trading.md