Run the FetchStats analysis once per selection

[CarsonDavis]

Category	Lines added	%
Tests	114	89.8%
Production code	13	10.2%

One AOI selection now makes one statistics request per layer, and unloading FetchStats mid-run silences it.

Closes #412

One selection, one request per layer

Previously, selecting an AOI queried every eligible visible layer twice, and the AOI progress readout counted doubled steps against a total it never cleanly reached.

The modern tool controller calls initialize() and then make(targetId), and initialize() itself already calls make(null), so the AOI subscription registered twice and every selection fired both listeners.

The fix: a made guard makes the second start a no-op, leaving one listener. Demo mission: yes, the demo is the modern layout and includes FetchStats.

Unloading the plugin mid-analysis goes quiet

Previously, a run in flight kept emitting progress, result, and skip messages onto the bus after teardown, so listeners heard from a plugin that no longer existed.

destroy() never dropped _api, and the four emit sites called it unconditionally.

The fix: destroy() nulls _api and the emits are optional-chained.

Classic Layout Stuff

The classic layout still answers a selection

Classic only calls initialize(), which is why the double query was modern-layout only and why the guard must not break the single start. It doesn't: one subscription there too, asserted by a test. Demo mission: no, only the test covers this.

AOI drives its progress readout off analysisProgress and only returns to idle on analysisReady, so tearing FetchStats down mid-run while AOI outlives it leaves AOI showing "running"; cancelling a run in flight is a separate issue.