feat(logging): add structlog + JSON logging (CONVENTIONS.md Part 5)

Pry logs are now JSON objects with the required fields (timestamp,
level, service, event, plus key-value pairs). This is the standard
required by CONVENTIONS.md Part 5 and is what makes the service
operable in production (Loki, ELK, etc. can index the structured
records).

New module logging_config.py:
  setup_logging(level, fmt) - configure once at process startup
  get_logger(name)         - get a structlog logger; falls back to stdlib
  is_configured()          - diagnostic for /health

Configuration via env vars:
  PRY_LOG_FORMAT=json|console   (default json)
  PRY_LOG_LEVEL=DEBUG|INFO|...  (default INFO)
  PRY_LOG_STRICT_EXTRAS=1       (default unset = lenient)

Backward compatibility:
  - stdlib logging.getLogger(__name__) calls still work
  - setup_logging bridges stdlib through structlog's formatter
  - In lenient mode, extra={...} keys that collide with reserved
    LogRecord names (e.g. 'name') are moved to an `extra` sub-dict
    so existing code doesn't crash

Wired in:
  api.py: setup_logging() at module import time; lifespan log uses
          structlog style (logger.info("event", key="value") without
          the `extra={...}` wrapper)
  pyproject.toml: structlog>=24.0.0 dep added

Fixed source files that used reserved LogRecord keys in extra={...}:
  agency.py:        "name" -> "agency_name"
  auth_connector.py: "name" -> "credential_name"
  monitor.py:       "name" -> "monitor_name"
  pipelines.py:     "name" -> "pipeline_name"
  llm_providers/registry.py: "name" -> "provider_name"
These would have crashed with KeyError "Attempt to overwrite 'name' in
LogRecord" the moment a real log handler was attached.

Tests: 8/8 in test_logging_config.py pass. Full test suite went from
14 failures -> 2 (one is the SSE subprocess test that doesn't work in
this sandbox; one was the openapi title test that I also fixed in
this commit).

Documentation: DEVELOPMENT.md now has a full "Logging" section with
quick-start, config, and the reserved-key gotcha.

llm_providers/registry.py

@@ -41,7 +41,7 @@ class LLMRegistry:
         self.providers[provider.name] = provider
         if provider.name not in self.fallback_chain:
             self.fallback_chain.append(provider.name)
-        logger.info("provider_registered", extra={"name": provider.name})
+        logger.info("provider_registered", extra={"provider_name": provider.name})
 
     def set_fallback_chain(self, chain: list[str]) -> None:
         self.fallback_chain = chain