feat: add strict tsconfig.base.json shared by all packages (E00-S01-T02)

Adds a strict base TypeScript config at the workspace root (ES2023 / NodeNext
/ strict family incl. noUncheckedIndexedAccess, exactOptionalPropertyTypes,
noImplicitOverride, useUnknownInCatchVariables, verbatimModuleSyntax per
Engineering-Standards) and gives every workspace package
(apps/server, packages/core, extensions/example) a tsconfig.json that extends
it. Each package gets a minimal src/index.ts placeholder so it compiles under
the base config (CJS-safe `export {}` until ESM boundaries land in T03).

Verified: every package typechecks and emits (js + d.ts + sourcemap) with the
pinned TypeScript 6.0.3; a strictness probe confirms the strict family fires.

Closes #155

tsconfig.base.json

@@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "target": "ES2023",
+    "lib": ["ES2023"],
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "strict": true,
+    "noUncheckedIndexedAccess": true,
+    "exactOptionalPropertyTypes": true,
+    "noImplicitOverride": true,
+    "useUnknownInCatchVariables": true,
+    "verbatimModuleSyntax": true,
+    "isolatedModules": true,
+    "esModuleInterop": true,
+    "forceConsistentCasingInFileNames": true,
+    "declaration": true,
+    "sourceMap": true,
+    "skipLibCheck": true
+  }
+}