Retire the AWT/JBR/JNI window backends, leaving only Tao

[kdroidFilter]

Tao becomes the single window backend. decorated-window-awt, decorated-window-jbr and decorated-window-jni are deleted with their native sources, API dumps, detekt baselines and GraalVM reachability metadata, along with the jni-demo sample (~10k lines removed).

Summary

• Modules removed: decorated-window-awt, decorated-window-jbr, decorated-window-jni, examples/jni-demo (+ settings.gradle.kts / apiValidation wiring, the jbr-api version-catalog entry, the jni/jbr native build steps and verify entries in build-natives / pre-merge / publish-maven).
• nucleus-application: drops the AWT application scope, window and dialog adapters; decorated-window-tao moves from compileOnly to api, since the backend is no longer a consumer choice and a missing runtime module would otherwise only fail at launch.
• Theme modules: the AWT overloads of MaterialDecoratedWindow / MaterialDecoratedDialog (M2 + M3) and JewelDecoratedWindow / JewelDecoratedDialog are gone — only the NucleusApplicationScope receivers remain, which also retires the LowPriorityInOverloadResolution / INVISIBLE_REFERENCE workarounds they required. material2's dialog existed only in AWT form, so it is ported to a NucleusApplicationScope receiver to keep parity with M3.
• taskbar-progress-tao: single Tao dispatch path instead of the AWT/Tao fork.
• core-runtime keeps WindowBackend.Awt: it still describes a plain Compose Desktop / Swing host that embeds Nucleus libraries. The plugin's jbr-api ProGuard keep and AOT unsealing workarounds also stay, since an app can still ship jbr-api itself.
• Demos migrated: scheduler-demo jni → Tao (drops the java.desktop/sun.* add-opens); service-management-demo swaps java.awt.EventQueue for rememberCoroutineScope().launch, because SMAppService completion handlers must now hop to the Tao main thread. The backend = NucleusBackend.Tao argument is dropped from the eight other demos.
• Docs: README (module table, project status, migration note), CLAUDE.md, and the ~37 dangling decorated-window-jni / -jbr / -awt references in Tao's KDoc and comments.
• Drive-by: rect-stress-demo and widget-demo are added to apiValidation.ignoredProjects alongside the other demos, fixing their pre-existing apiCheck failures.

Breaking changes

Removed from the public API (apiDump regenerated):

• NucleusBackend, LocalNucleusBackend, nucleusApplication(backend = …), NucleusApplicationScope.backend
• NucleusWindowUnsafe.awtWindow / awtDialog
• the ApplicationScope / receiver-less AWT overloads in the Material 2, Material 3 and Jewel modules

Migration: depend on nucleus.decorated-window-tao, drop the backend = argument, and replace AWT-typed window access and Compose Desktop's Window / Dialog / Tray with nucleusWindow, HostedWindow / HostedDialog and an AWT-free tray. Documented in the README's project-status section.

Docs describe the removal as landing in 2.6 — v2.5.0 is already tagged without it. Three occurrences to change if this should ship as 3.0.0 instead.

Test plan

• ./gradlew testClasses — every module and demo compiles
• ./gradlew test — all unit tests pass (NucleusApplicationScopeTest ported to the Tao scope)
• ./gradlew apiCheck / apiDump committed
• ./gradlew ktlintCheck detekt — clean, no baseline regeneration
• ./gradlew preMerge — green except plugin-build's LinuxSignerTest, which fails on gpg --gen-key locally and reproduces identically on a clean worktree at main (pre-existing, environmental)
• Headful run of scheduler-demo on macOS/JDK 25 — Jewel window renders with native traffic lights
• Headful run of service-management-demo on macOS/JDK 25 — Material 3 window renders, SMAppService: Available
• CI: Linux and Windows native builds + packaging