fix: allow spec reload

[MaxMichel2]

Summary

MockConfigRepository caches its parsed configuration forever after the first successful load, with no way to invalidate the cache and force a re-read. This is independent of the OpenAPI migration (tracked in the epic, #72) and can be picked up any time.

Current state

MockConfigRepository.loadConfiguration() (devview-networkmock-core/src/commonMain/kotlin/com/worldline/devview/networkmock/core/repository/MockConfigRepository.kt:201-254) checks cachedConfig (declared at :125) first and returns it immediately if present (:205-210), never re-reading the underlying resource. There is no method to clear this cache. In practice this means the mock configuration (mocks.json today, an OpenAPI spec after the migration in #72) can only ever be reloaded by restarting the process — there's no way for a developer to edit the config/spec file and see the change reflected without a full app restart, which is a meaningfully worse dev-loop than most things this tool is meant to speed up.

What to build

• Add a way to invalidate/clear cachedConfig, either as a new public method (e.g. invalidateCache() / reload()) or as a parameter on loadConfiguration() (e.g. loadConfiguration(forceReload: Boolean = false)).
• Decide whether this should be surfaced in the UI (e.g. the existing "Reset to Network" toolbar action pattern in NetworkMock.kt:131-158 is a reasonable precedent for adding a second toolbar action, "Reload config") or left as a repository-level API for now, and note the decision in the PR.
• Consider whether reloading needs to also re-run registerEndpoints/response-discovery downstream (NetworkMockViewModel.loadConfiguration(), devview-networkmock/src/commonMain/kotlin/com/worldline/devview/networkmock/viewmodel/NetworkMockViewModel.kt:138-193) — likely yes, since a changed config could add/remove/rename operations.

Acceptance criteria

• There is a way to force MockConfigRepository to re-read and re-parse its underlying resource after the first load.
• Calling the invalidation path and then reloading picks up changes to the underlying file (test with a resource loader stub that returns different content on a second call).
• If surfaced in the UI, it follows the existing "Reset to Network" action pattern for consistency.

Files likely touched

• devview-networkmock-core/src/commonMain/kotlin/com/worldline/devview/networkmock/core/repository/MockConfigRepository.kt
• devview-networkmock/src/commonMain/kotlin/com/worldline/devview/networkmock/NetworkMock.kt (if surfaced in the UI)
• devview-networkmock/src/commonMain/kotlin/com/worldline/devview/networkmock/viewmodel/NetworkMockViewModel.kt (if surfaced in the UI)