Add .npmrc: map @jsr scope to JSR registry + legacy-peer-deps

Fixes local `npm install` failures on the build machine:
- @jsr:registry=https://npm.jsr.io — the Nostrify stack depends on JSR packages
  (@jsr/std__encoding, etc.) that don't exist on registry.npmjs.org; without
  this mapping npm 404s. The lockfile already resolves them via npm.jsr.io, but
  a fresh install from package.json needs the scope registry configured.
- legacy-peer-deps=true — resolves the long-standing benign peer-range lags
  (e.g. react-day-picker@8 peers date-fns 2/3 while the app uses date-fns 4)
  the same way the hosted build environment does, instead of ERESOLVE.

Co-authored-by: shakespeare.diy <assistant@shakespeare.diy>

.npmrc

@@ -0,0 +1,11 @@
+# The Nostrify stack depends on packages published to JSR (the Deno registry),
+# exposed to npm under the `@jsr/*` scope (e.g. @jsr/std__encoding). npm must be
+# told these come from JSR's npm-compatible registry, otherwise it looks them up
+# on registry.npmjs.org and fails with a 404.
+@jsr:registry=https://npm.jsr.io
+
+# This project has a couple of long-standing benign peer-range lags (e.g.
+# react-day-picker@8 lists date-fns 2/3 as a peer while we use date-fns 4).
+# legacy-peer-deps lets `npm install` resolve like the build environment does,
+# instead of hard-failing on ERESOLVE.
+legacy-peer-deps=true