fix(csp): ship the interface strings as a JSON data block, not an inline script

base.html.j2 set window.I18N from an executable inline <script>. A host
CSP can only allow an inline script by hash or by 'unsafe-inline', and this
script's content changes with every language, so no hash can cover it.
Infinito.Nexus serves the dashboard with a hash-based script-src-elem
whenever its logout feature is off, and there the script was blocked:
every page logged "Executing inline script violates the following Content
Security Policy directive 'script-src-elem ...'" and window.I18N stayed
undefined.

The strings now ship as <script id="i18n" type="application/json">, which
the browser does not execute and CSP does not govern; modal.js parses the
block before its first use. tojson escapes <, > and &, so a string that
contains "</script>" cannot end the block early.

Integration tests require that a page ships no executable inline script
and that a catalogue string containing "</script>" survives the round trip
through the block.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/integration/test_app_routes.py

@@ -1,5 +1,6 @@
 import json
 import os
+import re
 import shutil
 import subprocess
 import sys
@@ -111,6 +112,37 @@ class TestEscaping(AppRouteMixin, unittest.TestCase):
         self.assertIn("<script>alert('config')", body)
 
 
+class TestContentSecurityPolicy(AppRouteMixin, unittest.TestCase):
+    def test_page_ships_no_executable_inline_script(self):
+        body = self.client.get("/de/").get_data(as_text=True)
+
+        inline = [
+            tag
+            for tag in re.findall(r"<script\b[^>]*>", body)
+            if "src=" not in tag and 'type="application/json"' not in tag
+        ]
+
+        self.assertEqual(
+            inline,
+            [],
+            "a host CSP can only hash an inline script whose content it knows, "
+            "and this one changes with every language",
+        )
+
+    def test_interface_strings_ship_as_a_json_data_block(self):
+        i18n._catalogs["de"] = {"Open": "</script><script>alert(1)</script>"}
+
+        body = self.client.get("/de/").get_data(as_text=True)
+        block = re.search(
+            r'<script id="i18n" type="application/json">(.*?)</script>', body, re.S
+        )
+
+        self.assertIsNotNone(block)
+        self.assertEqual(
+            json.loads(block.group(1))["Open"], "</script><script>alert(1)</script>"
+        )
+
+
 class TestApodBackground(AppRouteMixin, unittest.TestCase):
     def setUp(self):
         super().setUp()