chore(tsconfig): migrate off deprecated baseUrl

TypeScript 6 deprecates `baseUrl` in favor of resolving `paths`
relative to the file that defines them. Earlier commit (bde40e4)
silenced the warning via `ignoreDeprecations`; this commit does
the actual migration so the warning goes away on its merits.

Changes:

1. tsconfig.base.json: drop `baseUrl: "."`. Add an explicit `./`
   prefix to every `paths` entry so they resolve relative to the
   base config's location (the repo root) — same behavior as
   before, but no baseUrl needed. (TypeScript requires path entries
   to be relative or absolute when baseUrl is absent; bare paths
   like "packages/..." are not allowed.)
2. apps/web-next/tsconfig.json: drop baseUrl. The `@/*` mapping's
   target was already "./src/*" — relative-from-tsconfig-file is
   the new default, so no other change.
3. apps/cms/tsconfig.json: same — drop baseUrl, paths already use
   "./" prefix.
4. apps/storybook/tsconfig.json: same.
5. apps/web-tanstack/tsconfig.json: same.

Generator templates (turbo/generators/templates/feature/tsconfig.json.hbs)
already omit baseUrl, so future-generated features inherit the new
posture.

Reverts the ignoreDeprecations setting added in bde40e4 — no longer
needed.

Verified:
- pnpm typecheck 14/14
- pnpm lint 15/15
- pnpm test 26/26

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

apps/storybook/tsconfig.json

@@ -1,7 +1,6 @@
 {
   "extends": "@repo/core-typescript/react-library.json",
   "compilerOptions": {
-    "baseUrl": ".",
     "paths": {
       "@/*": ["./src/*"]
     }