core: consolidate shared infrastructure into core package

Moves effect logging, observability, runtime utilities, flags, installation
version info, and process utilities from opencode to core package. This
enables better code sharing across packages and establishes core as the
single source of truth for foundational utilities.

All internal imports updated to use @opencode-ai/core paths for consistency.

packages/core/src/global.ts

@@ -3,6 +3,24 @@ import { xdgData, xdgCache, xdgConfig, xdgState } from "xdg-basedir"
 import os from "os"
 import { Context, Effect, Layer } from "effect"
 
+const app = "opencode"
+const data = path.join(xdgData!, app)
+const cache = path.join(xdgCache!, app)
+const config = path.join(xdgConfig!, app)
+const state = path.join(xdgState!, app)
+
+export const Path = {
+  get home() {
+    return process.env.OPENCODE_TEST_HOME ?? os.homedir()
+  },
+  data,
+  bin: path.join(cache, "bin"),
+  log: path.join(data, "log"),
+  cache,
+  config,
+  state,
+}
+
 export namespace Global {
   export class Service extends Context.Service<Service, Interface>()("@opencode/Global") {}
 
@@ -19,23 +37,14 @@ export namespace Global {
   export const layer = Layer.effect(
     Service,
     Effect.gen(function* () {
-      const app = "opencode"
-      const home = process.env.OPENCODE_TEST_HOME ?? os.homedir()
-      const data = path.join(xdgData!, app)
-      const cache = path.join(xdgCache!, app)
-      const cfg = path.join(xdgConfig!, app)
-      const state = path.join(xdgState!, app)
-      const bin = path.join(cache, "bin")
-      const log = path.join(data, "log")
-
       return Service.of({
-        home,
-        data,
-        cache,
-        config: cfg,
-        state,
-        bin,
-        log,
+        home: Path.home,
+        data: Path.data,
+        cache: Path.cache,
+        config: Path.config,
+        state: Path.state,
+        bin: Path.bin,
+        log: Path.log,
       })
     }),
   )