fix(agui): cancel MVC subscription on disconnect

[logicwu0]

Summary

• cancel the MVC event subscription on SSE error or timeout when interruptOnDisconnect is enabled
• create the subscriber before disconnect callbacks are registered, so cancellation is safe before the event stream is subscribed
• preserve the existing behavior when automatic interruption is disabled
• add regression tests for SSE error, timeout, and the disabled configuration

Why this is still needed

The behavior reported on 2.0.1 had more than one lifecycle problem. #2646 fixed one part by preventing the conflicting RUN_ERROR followed by RUN_FINISHED sequence.

However, that change did not cancel the MVC Reactor subscription when the SSE connection fails or times out. On the latest main (bf7b7dae), the controller only interrupts the agent. The active-run entry is still released by the event stream's doFinally, so an immediate request on the same thread can still be rejected while upstream termination is delayed.

Disposing the subscription after requesting interruption triggers the cancellation lifecycle immediately and lets doFinally release the thread.

Tests

• SSE error cancels the active subscription and allows an immediate second run
• SSE timeout cancels the active subscription and allows an immediate second run
• disabling interruptOnDisconnect keeps the first run active

Fixes #2782

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...tscope/spring/boot/agui/mvc/AguiMvcController.java	85.71%	3 Missing ⚠️

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