fix(memory): recover from panics during mission export

[fank]

Summary

• memory.Backend.EndMission now catches panics from the builder or gzip encoder and converts them to a returned error.
• Logs the stack trace at ERROR level so a panic still leaves a forensic trail.
• Does not attempt to catch runtime.throw / OOM — those are a kernel/container problem, not a panic.

Why

Previously any recoverable panic during buildExportUnlocked or writeGzipJSON would propagate straight out of the sync :MISSION:SAVE: handler and kill the ArmA host. Even once the handler is async (see #159), the worker goroutine still needs a clean error return instead of an unrecovered panic — the new :MISSION:SAVED: callback path relies on EndMission returning an error rather than panicking.

Test plan

• go test ./internal/storage/memory/...
• New test TestEndMission_RecoversFromBuildPanic exercises the recover path — verified to panic before the fix and return a descriptive error after.

[gemini-code-assist]

Code Review

This pull request introduces panic recovery in the EndMission method of the memory storage backend to prevent host process crashes during mission export, along with a corresponding test case. The review feedback correctly identifies that the current implementation leaves the backend in an inconsistent state when a panic occurs, as the necessary cleanup and state reset logic are bypassed.

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/OCAP2/extension/v5/internal/storage/memory	99.24% (+0.02%)	👍

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/OCAP2/extension/v5/internal/storage/memory/memory.go	100.00% (ø)	227 (+6)	227 (+6)	0

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/OCAP2/extension/v5/internal/storage/memory/memory_test.go