feat(security,ui): self-host React deps, Tailwind, fonts; strict CSP; local QR; better selection state

Replace CDN React/ReactDOM/Babel with local libs; remove Babel and inline scripts
Build Tailwind locally, add safelist; switch to assets/tailwind.css
Self-host Font Awesome and Inter (CSS + woff2); remove external font CDNs
Implement strict CSP (no unsafe-inline/eval; scripts/styles/fonts from self)
Extract inline handlers; move PWA scripts to external files
Add local QR code generation (qrcode lib) and remove api.qrserver.com
Improve SessionTypeSelector visual selection (highlighted background and ring)
Keep PWA working with service worker and offline assets
Refs: CSP hardening, offline-first, no external dependencies

node_modules/qrcode/lib/core/polynomial.js

@@ -0,0 +1,62 @@
+const GF = require('./galois-field')
+
+/**
+ * Multiplies two polynomials inside Galois Field
+ *
+ * @param  {Uint8Array} p1 Polynomial
+ * @param  {Uint8Array} p2 Polynomial
+ * @return {Uint8Array}    Product of p1 and p2
+ */
+exports.mul = function mul (p1, p2) {
+  const coeff = new Uint8Array(p1.length + p2.length - 1)
+
+  for (let i = 0; i < p1.length; i++) {
+    for (let j = 0; j < p2.length; j++) {
+      coeff[i + j] ^= GF.mul(p1[i], p2[j])
+    }
+  }
+
+  return coeff
+}
+
+/**
+ * Calculate the remainder of polynomials division
+ *
+ * @param  {Uint8Array} divident Polynomial
+ * @param  {Uint8Array} divisor  Polynomial
+ * @return {Uint8Array}          Remainder
+ */
+exports.mod = function mod (divident, divisor) {
+  let result = new Uint8Array(divident)
+
+  while ((result.length - divisor.length) >= 0) {
+    const coeff = result[0]
+
+    for (let i = 0; i < divisor.length; i++) {
+      result[i] ^= GF.mul(divisor[i], coeff)
+    }
+
+    // remove all zeros from buffer head
+    let offset = 0
+    while (offset < result.length && result[offset] === 0) offset++
+    result = result.slice(offset)
+  }
+
+  return result
+}
+
+/**
+ * Generate an irreducible generator polynomial of specified degree
+ * (used by Reed-Solomon encoder)
+ *
+ * @param  {Number} degree Degree of the generator polynomial
+ * @return {Uint8Array}    Buffer containing polynomial coefficients
+ */
+exports.generateECPolynomial = function generateECPolynomial (degree) {
+  let poly = new Uint8Array([1])
+  for (let i = 0; i < degree; i++) {
+    poly = exports.mul(poly, new Uint8Array([1, GF.exp(i)]))
+  }
+
+  return poly
+}