[AZ-494] Enable JWT iss/aud validation with fail-fast startup

Option B per user decision: production ships with empty Jwt.Issuer /
Jwt.Audience in appsettings.json so the API process refuses to start
unless JWT_ISSUER + JWT_AUDIENCE env vars are supplied. Development
ships with grep-friendly DEV-ONLY- placeholders so local + docker
flows keep working unchanged.

AuthenticationServiceCollectionExtensions flips ValidateIssuer +
ValidateAudience to true and wires ValidIssuer / ValidAudience via a
new ResolveRequiredOrThrow helper that all three required values
(secret, iss, aud) now share. JwtTokenFactory.Create + CreateExpired
gain optional iss / aud parameters (default null) so existing call
sites compile unchanged. JwtTestHelpers adds MintAuthenticated /
MintExpired wrappers that resolve iss + aud from env, plus
ResolveIssuerOrThrow / ResolveAudienceOrThrow. PerfBootstrap.MintToken
+ Program.cs JWT bootstrap migrated to the new surface so the perf
harness and the integration runner both validate against the same
contract.

Adds 4 fail-fast unit tests (missing/empty issuer + audience), 2
negative integration scenarios (WrongIssuer_Returns401,
WrongAudience_Returns401), and re-tags every existing integration
mint site via MintAuthenticated.

Compose, .env.example, run-tests.sh, run-performance-tests.sh all
load + export JWT_ISSUER + JWT_AUDIENCE alongside JWT_SECRET.

Resolves F-AUTH-2 (security_report.md + owasp_review.md). AC-7
(cross-repo suite/_docs/10_auth.md write) deferred — outside this
workspace; tracked in deploy_cycle2.md R3 follow-up.

Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

@@ -16,3 +16,17 @@ GOOGLE_MAPS_API_KEY=
 #
 # Test/CI runs may use a clearly tagged TEST-ONLY value (still >=32 bytes).
 JWT_SECRET=
+
+# JWT issuer / audience claims (AZ-494). Both are REQUIRED — the API
+# fails fast at startup if either is unset or whitespace-only.
+#
+# Production values MUST be confirmed by the admin team before deploy
+# (the admin API stamps the `iss` claim; satellite-provider validates
+# the `aud` claim). For local dev these can use the DEV-ONLY values
+# baked into appsettings.Development.json — leave blank to fall back.
+#
+# Example values (NEVER use these in prod):
+#   JWT_ISSUER=DEV-ONLY-iss-admin-azaion-local
+#   JWT_AUDIENCE=DEV-ONLY-aud-satellite-provider
+JWT_ISSUER=
+JWT_AUDIENCE=