refactor(core): separate portable core from native runtime (#2451)

Create easytier-core as the portable owner of configuration,
connectivity, tunnels, peer and routing state, gateways, management,
the data plane, and instance lifecycle. Keep operating-system
integration, native protocol engines, process startup, and presentation
in easytier behind explicit Host capability adapters.

Create easytier-proto to own schemas, generated RPC types, descriptors,
and feature-scoped protocol slices. Remove runtime protobuf reflection
from core while preserving unknown route-peer fields across forwarding.

Normalize instance construction through CoreInstance, CoreHostAdapters,
CoreProcessRuntime, and InstanceManager. Make the runtime config store
the only authoritative mutable configuration after startup.

Move the portable TCP/UDP data plane into core and extract a generic
OperationBroker for completion, cancellation, disposal, and capacity
accounting. Expose the session-based FFI v2 completion API and keep the
WASI guest ABI, wire schemas, and adapters with core.

Migrate CLI, GUI, web, FFI, Android JNI, OHOS, uptime, and mobile
consumers to the shared manager and core state. Add explicit user/web
config ownership and revision-aware web reconciliation.

Preserve configuration, wire, and management behavior while fixing
regressions discovered by the full platform and integration matrix:

- inherit advertised relay capabilities in foreign networks;
- refresh OSPF peer state immediately after runtime config changes;
- restore CLI GlobalCtx event output without forcing GUI logging;
- retain legacy encryption names and standalone RPC tunnel metadata;
- restore ICMP host composition and fragmented UDP handling;
- use portable 64-bit atomics on 32-bit MIPS targets; and
- retain discarded operations until late cancellation completes.

Validate the refactor across 45 GitHub checks, including Linux, macOS,
Windows, FreeBSD, web, GUI, Android, OHOS, feature profiles, and
three-node and subnet-proxy integration tests.

BREAKING CHANGE: internal Rust module paths are not preserved. Legacy
native data-plane APIs are replaced by the session-based FFI v2 API.
The dedicated Android data-plane wrapper is removed.

CONTEXT.md

@@ -0,0 +1,23 @@
+# EasyTier Domain Context
+
+## Module layers
+
+`easytier-core` layers dependencies from `foundation` upward through the
+portable networking domains. `foundation` contains infrastructure Modules
+that have no dependency on a networking domain and may be used by any higher
+layer.
+
+## Operation broker
+
+An operation broker owns the lifecycle of asynchronous work submitted by an
+external caller to core. It allocates opaque operation IDs, arbitrates
+completion, cancellation, and disposal, retains terminal outcomes, and
+publishes a batch-drainable completion queue.
+
+The broker does not interpret operation kinds, outcomes, resources, wire
+formats, or domain errors. Each domain Module owns those semantics and composes
+the broker under the same lock as any state that must change atomically with an
+operation transition.
+
+Host capability operations use a separate seam. They turn Host readiness into
+Rust task wakeups and do not share the caller-to-core broker state machine.