fix: Claude CLI conversation state survives resets and leaks old history into new chats

[sam-saffron-jarvis]

What

Add a ResetConversation() hook to ClaudeBinProvider that clears the persisted Claude CLI resume state (sessionID and messagesSent) so fresh conversations do not reuse the previous Claude session. Also add a regression test covering the reset behavior.

Why

Engine.ResetConversation() already forwards resets to providers that implement a reset hook, but ClaudeBinProvider was not implementing one even though it caches resume state across turns. That let supposedly fresh conversations keep resuming the old Claude CLI session, skip re-sending the full prompt/system instructions, and leak stale context into new chats.

[SamSaffron]

Closing in favor of consolidated local changeset on branch pr-consolidation. The change from this PR was folded in along with: #387, #389, #390, #391, #400, #401, #402, #403, #404. Build and full test suite pass.