fix: read instance attributes in api_bootstrapper_config

[lesnik512]

Bug

Settings.api_bootstrapper_config built its LitestarConfig from the module-global settings singleton instead of self:

@property
def api_bootstrapper_config(self) -> LitestarConfig:
    return LitestarConfig(
        service_name=settings.service_name,   # ← global, not self
        ...
    )

So any Settings instance other than the singleton — or any access during the singleton's own construction — silently produced the singleton's values rather than its own.

Fix

Every field now reads self.*.

Test (TDD — failing first)

Added tests/test_settings.py, which constructs a Settings(service_name="custom-service", service_version="9.9.9") and asserts api_bootstrapper_config reflects the instance.

• Before the fix (RED): assert 'Litestar template' == 'custom-service' — fails, proving the global leak.
• After the fix (GREEN): passes.

20 passed, 100% coverage.

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