fix: switch to source-first internal package pattern

Remove composite mode and project references. Internal packages
(@zpan/shared) export .ts source files directly via package.json
exports field. Bundlers (Vite, wrangler, tsup) handle .ts at build
time, and tsc --noEmit resolves cross-package imports through the
exports field without needing a build step.

This eliminates TS6305 errors when typechecking server/web after
modifying shared, which was breaking every PR that imported from
@zpan/shared/types or @zpan/shared/schemas.

packages/server/tsconfig.json

@@ -1,12 +1,8 @@
 {
   "extends": "../../tsconfig.base.json",
   "compilerOptions": {
-    "composite": true,
-    "outDir": "dist",
-    "rootDir": "src",
     "types": ["@cloudflare/workers-types"]
   },
   "include": ["src"],
-  "exclude": ["src/**/*.cf-test.ts", "src/test/apply-migrations.ts"],
-  "references": [{ "path": "../shared" }]
+  "exclude": ["src/**/*.cf-test.ts", "src/test/apply-migrations.ts"]
 }

packages/shared/tsconfig.json

@@ -1,9 +1,4 @@
 {
   "extends": "../../tsconfig.base.json",
-  "compilerOptions": {
-    "composite": true,
-    "outDir": "dist",
-    "rootDir": "src"
-  },
   "include": ["src"]
 }

packages/web/tsconfig.json

@@ -4,13 +4,10 @@
     "declaration": false,
     "declarationMap": false,
     "jsx": "react-jsx",
-    "outDir": "dist",
-    "rootDir": "src",
     "baseUrl": ".",
     "paths": {
       "@/*": ["./src/*"]
     }
   },
-  "include": ["src"],
-  "references": [{ "path": "../shared" }]
+  "include": ["src"]
 }