fix: use effect 4.x matching opencode (#270)

fix: use effect 4.x matching opencode to fix cross-module Effect incompatibility

Effect 3.x uses unique Symbol for TypeId; Effect 4.x uses the plain string
'~effect/Effect'. Running Effect.runPromise from a bundled 3.x instance on
a 4.x Effect object fails with 'Not a valid effect: {}' because isEffect()
uses a Symbol lookup that cannot find the string-keyed property.

Pinning effect to 4.0.0-beta.48 (matching opencode) and adding a local
tsconfig.json with moduleResolution:bundler so DTS generation resolves the
package exports correctly.

Author: mrsimpson

packages/opencode-plugin/package.json

@@ -24,7 +24,7 @@
     "format": "prettier --write ."
   },
   "dependencies": {
-    "effect": ">=3.0.0",
+    "effect": "4.0.0-beta.48",
     "zod": "^4.1.8"
   },
   "devDependencies": {

packages/opencode-plugin/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "moduleResolution": "bundler",
+    "module": "ESNext"
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}