fpaste: add register command for public certificate enrollment

- Add register command to obtain client cert from server
- Solve PoW challenge, receive PKCS#12 bundle
- Extract cert/key, optionally update config (--configure)
- Fix registration to work without PKI_ENABLED (only needs PKI_CA_PASSWORD)
- Add skip_enabled_check param to get_ca_info() for registration path
- Update docs: README examples, API header name fix (X-Fingerprint-SHA1)

app/pki.py

@@ -736,9 +736,12 @@ def is_certificate_valid(fingerprint: str) -> bool:
 # ─────────────────────────────────────────────────────────────────────────────
 
 
-def get_ca_info() -> dict | None:
+def get_ca_info(skip_enabled_check: bool = False) -> dict | None:
     """Get CA information for status endpoint.
 
+    Args:
+        skip_enabled_check: If True, skip the PKI_ENABLED check (for registration)
+
     Returns:
         Dict with CA info or None if no CA exists
     """
@@ -746,7 +749,7 @@ def get_ca_info() -> dict | None:
 
     from app.database import get_db
 
-    if not current_app.config.get("PKI_ENABLED"):
+    if not skip_enabled_check and not current_app.config.get("PKI_ENABLED"):
         return None
 
     db = get_db()