Makes long-running Apps tool APIs run properly in background (BL-16350)

[JohnThomson]

Several Apps tool APIs, especially Build, were made to kick off a background task and then return; task completion signaled by websocket.
Enhanced so if you return to the tool and build is still running, it gets back into a state indicating the progress of the build.
Also, Build is now more appropriately enabled; you don't have to do Customize first if all the required settings are already known.

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This change is 

Devin review

[greptile-apps]

Greptile Summary

This PR converts the three long-running Apps tool APIs (prepare, build, install) from synchronous blocking handlers into fire-and-forget Task.Run background tasks that complete via a new actionComplete websocket event, and adds server-side progress state so the UI can restore its busy indicator after switching tabs mid-build.

• C# backend: TryBeginAction uses Interlocked.CompareExchange for an atomic concurrency guard; volatile fields expose the latest progress stage/percent through GetStatus(); ClearAction + SendActionCompleteEvent are called in the correct order in finally blocks; requiresSync: false is applied to all five read/action endpoints.
• TypeScript frontend: busyActionRef tracks the latest action in async contexts; the isActive effect now snapshots server state before resetting the BloomPUB cache (skipping the reset when a build is in progress); a new useSubscribeToWebSocketForStringMessage handler processes actionComplete events; refreshStatus recovers stale busy state on remount.
• UI: The requiresSubscription overlay no longer flashes while featureStatus is loading; the Build button no longer requires a detected change (buildIsNeeded removed) — it is enabled whenever prepare has run and required settings are present.

Important Files Changed

Filename	Overview
src/BloomExe/Publish/Rab/RabPublishApi.cs	Replaced synchronous RegisterAsyncEndpointHandler calls with fire-and-forget Task.Run pattern; TryBeginAction provides atomic concurrency guard; previous review concerns addressed
src/BloomExe/Publish/Rab/RabProjectService.cs	Added TryBeginAction (Interlocked.CompareExchange), ClearAction, SendActionCompleteEvent; volatile progress fields; GetStatus exposes active action/progress; Prepare() early-return path does not propagate failure to succeeded flag
src/BloomExe/Publish/Rab/RabProjectModels.cs	Added ActiveAction, ActiveActionProgressStage, ActiveActionProgressPercent to RabProjectStatus DTO for mid-session remount recovery
src/BloomBrowserUI/publish/Apps/useAppBuilderPublisherScreen.ts	Added busyActionRef, remount-recovery logic in refreshStatus, tab-activation effect reworked, runAction switches to post, actionComplete websocket subscription added
src/BloomBrowserUI/publish/Apps/appBuilderShared.ts	Extended IAppBuilderStatus/IAppBuilderStatusApi with activeAction/progress fields; dual-casing normalization in normalizeStatus; kAppBuilderActionCompleteEventId constant added
src/BloomBrowserUI/publish/Apps/AppPublisherScreen.tsx	Removed buildIsNeeded from Build button enabled guard so the button is available whenever settings are present, not only when a change is detected
src/BloomBrowserUI/react_components/requiresSubscription.tsx	Fixed overlay flashing while featureStatus is loading by adding featureStatus === undefined guard
src/BloomExe/web/controllers/FeatureStatusApi.cs	Added requiresSync: false to the feature-status endpoint; safe read-only handler

_{Reviews (9): Last reviewed commit: "Makes long-running Apps tool APIs run pr..." | Re-trigger Greptile}

[andrew-polk]

devin found some stuff...

@andrew-polk reviewed 8 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on JohnThomson).

[JohnThomson]

@JohnThomson made 1 comment and resolved 1 discussion.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on JohnThomson).

[JohnThomson]

Devin seems to be (finally!) happy as of 724ef4a

@JohnThomson made 1 comment.
Reviewable status: 5 of 8 files reviewed, all discussions resolved (waiting on andrew-polk).

[andrew-polk]

@andrew-polk reviewed 3 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on JohnThomson).

[andrew-polk]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on JohnThomson).