Adopt sk.ainet.multiplatform from SKaiNET-build-logic (asr-domain, transformer-core, llm-core) - #434

…ansformer-core, llm-core)

Migrates the three modules that downstream ASR cartridges and asr-cli
actually consume (asr-domain, transformer-core, llm-core) to the
published sk.ainet.multiplatform/sk.ainet.npm-pins convention plugins
from github.com/SKaiNET-developers/SKaiNET-build-logic, replacing their
hand-rolled plugins{}/kotlin{ android{...}; jvm(); ...; js{browser()}/
wasmJs{browser()} } target boilerplate with id("sk.ainet.multiplatform")
+ a per-module skainet { namespace = ... } block and a gradle.properties
skainet.targets declaration.

Retires this repo's own buildSrc entirely: it existed solely to provide
sk.ainet.transformers.bom-coverage, which is now consumed from the same
shared plugin jar (already reconciled to include this repo's own
POM-completeness fail-fast check -- both implementations' logic is kept,
not one picked over the other). llm-bom's own build.gradle.kts needed
zero changes -- id("sk.ainet.transformers.bom-coverage") now resolves
externally via pluginManagement.plugins{} instead of from buildSrc.

Two real per-module deltas handled, not blindly forced to the plugin's
defaults:
- llm-core wants androidNativeArm32 only, not the androidNativeArm64 the
  plugin's androidNative target group would also add -- declared
  manually in the module's own kotlin{} block instead (alongside its
  already-hand-wired registryBasedMain/nativeMain source-set hierarchy,
  kotlin.mpp.applyDefaultHierarchyTemplate=false, untouched).
- llm-core opts out of the plugin's explicitApi=true default
  (DecoderGgufWeightLoader.kt has a handful of pre-existing declarations
  missing visibility modifiers, never caught before since explicit API
  mode was never on here -- fixing that source is a separate, smaller
  follow-up, not folded into this build-tooling migration).

The other 24-ish modules in this repo (llm-agent, llm-inference/*,
llm-runtime/*, etc.) are NOT migrated here -- several have much more
extensive custom source-set wiring (llm-runtime/kgemma: 257 lines/14
custom source sets; llm-runtime/kllama: 220 lines/21) that deserves
individual, careful handling rather than a batch pass, and none of them
are on the dependency path cartridge releases/publishing or asr-cli
actually need.

Verified: full multi-project configuration green; asr-domain/
transformer-core/llm-core compile clean on jvm + linuxX64 (+
androidNativeArm32 for llm-core); real jvmTest green for transformer-core
and llm-core; publishToMavenLocal green; and -- the real proof -- all
three downstream consumers (asr-whisper-iree-cartridge,
asr-moonshine-iree-cartridge, asr-cli) verified green against the
mavenLocal-published result via their own full `check` (+ asr-cli's
shadowJar).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>