feat: make all operational constants configurable via bouncer.toml

Replace hardcoded values across network, captcha, email, and cert
modules with BouncerConfig fields. All values have safe defaults
and are overridable in the [bouncer] section of the config file.

Configurable: probation_seconds, backoff_steps, nick_timeout,
rejoin_delay, http_timeout, captcha_poll_interval/timeout,
email_poll_interval/max_polls/request_timeout, cert_validity_days.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_cert.py

@@ -53,6 +53,15 @@ class TestGenerateCert:
         assert pem1 == pem2
         assert fp1 != fp2  # New cert = new fingerprint
 
+    def test_custom_validity_days(self, data_dir: Path) -> None:
+        import datetime
+        from cryptography import x509 as x509_mod
+        pem = generate_cert(data_dir, "libera", "testnick", validity_days=365)
+        cert_data = pem.read_bytes()
+        cert_obj = x509_mod.load_pem_x509_certificate(cert_data)
+        delta = cert_obj.not_valid_after_utc - cert_obj.not_valid_before_utc
+        assert 364 <= delta.days <= 366
+
 
 class TestFingerprint:
     def test_format(self, data_dir: Path) -> None: