case 4711 - JWT signing key generated by the server; AYANOVA_JWT_SECRET removed

The LAN/IIS and Linux templates shipped a placeholder secret printed in the
manual, and installs that kept it signed logins with a public key; any setting
also invited short or reused values (security review F1). The setting is now
ignored (one warning at boot if still present): the server generates a key once
(48 random bytes) into jwt-signing.key in the data folder (beside the app if
there is none; owner-only on Linux) and reuses it, so sign-ins also survive a
restart where the server used to make a new key each boot (standalone, Linux
desktop). If the file cannot be used, a temporary key is used for that run.

Templates and dev launch configs drop the setting; manual updated (key page
rewritten, setting steps removed from install pages); changelog line.

Checked locally: token forged with the old placeholder 401; key file created
and reused after restart (old token 200); auth and 2FA tests pass.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.vscode/launch.json

@@ -55,7 +55,6 @@
       "env": {
         //############ PERPETUAL BLOCK ######################
         //   "ASPNETCORE_ENVIRONMENT": "Development",
-        "AYANOVA_JWT_SECRET": "1111111MyRandom32CharacterSecret",
         "AYANOVA_LOG_LEVEL": "Info",
         //"AYANOVA_LOG_LEVEL": "Debug",
         //"AYANOVA_LOG_LEVEL": "Trace",
@@ -111,7 +110,6 @@
         //############ SUBSCRIPTION MODE BLOCK ######################
         //   "ASPNETCORE_ENVIRONMENT": "Development",        
         //"AYANOVA_REPORT_RENDERING_TIMEOUT":"1",
-        "AYANOVA_JWT_SECRET": "1111111MyRandom32CharacterSecret",
         "AYANOVA_LOG_LEVEL": "Info",
         //"AYANOVA_LOG_LEVEL": "Debug",
         //"AYANOVA_LOG_LEVEL": "Trace",