chore(tsconfig): silence baseUrl-deprecation warning via ignoreDeprecations

TypeScript 6 deprecates `baseUrl` in favor of resolving `paths`
relative to the tsconfig file's directory. The repo's path mappings
in tsconfig.base.json currently rely on baseUrl: "." to resolve
"packages/<feature>/src/index.ts" entries against the repo root,
and four app tsconfigs (web-next, cms, web-tanstack, storybook) use
baseUrl: "." for their own "@/*" → "./src/*" mappings.

Migrating away from baseUrl is a separate cleanup — for now, set
"ignoreDeprecations": "6.0" in the base config so the warning
clears across every config that extends it (extends merges
compilerOptions). This is exactly what TypeScript's own docs
recommend for projects that intend to keep the option until 7.0.

Verified: pnpm typecheck 14/14, pnpm lint 15/15.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tsconfig.base.json

@@ -1,6 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/tsconfig",
   "compilerOptions": {
+    "ignoreDeprecations": "6.0",
     "baseUrl": ".",
     "paths": {
       "@repo/core-shared": ["packages/core-shared/src/index.ts"],