feat: add cloudflare and ddns install extras for backend consistency (#14)

- Add cloudflare and ddns optional-dependency extras (empty markers,
  these backends use core deps httpx/dnspython)
- Update [all] comment to reference all four backends
- Document all backend extras in README and getting-started guide

Signed-off-by: Igor Racic <iracic82@gmail.com>

Author: iracic82

README.md

@@ -29,8 +29,11 @@ pip install dns-aid[cli]
 # With MCP server for AI agents
 pip install dns-aid[mcp]
 
-# With Route 53 backend
-pip install dns-aid[route53]
+# With a specific backend
+pip install dns-aid[route53]      # AWS Route 53
+pip install dns-aid[cloudflare]   # Cloudflare DNS
+pip install dns-aid[infoblox]     # Infoblox BloxOne
+pip install dns-aid[ddns]         # RFC 2136 Dynamic DNS (BIND, PowerDNS)
 
 # Everything
 pip install dns-aid[all]

docs/getting-started.md

@@ -34,10 +34,13 @@ pip install -e ".[all]"
 ### Option 2: Install specific components
 
 ```bash
-pip install -e "."           # Core library only
-pip install -e ".[cli]"      # Core + CLI
-pip install -e ".[mcp]"      # Core + MCP server
-pip install -e ".[route53]"  # Core + Route 53 backend
+pip install -e "."              # Core library only
+pip install -e ".[cli]"         # Core + CLI
+pip install -e ".[mcp]"         # Core + MCP server
+pip install -e ".[route53]"     # Core + Route 53 backend
+pip install -e ".[cloudflare]"  # Core + Cloudflare backend
+pip install -e ".[infoblox]"    # Core + Infoblox BloxOne backend
+pip install -e ".[ddns]"        # Core + RFC 2136 Dynamic DNS backend
 ```
 
 ## Quick Test (No AWS needed)

pyproject.toml

@@ -55,6 +55,12 @@ route53 = [
 infoblox = [
     # Uses httpx from core deps
 ]
+cloudflare = [
+    # Uses httpx from core deps
+]
+ddns = [
+    # Uses dnspython from core deps
+]
 jws = [
     # JWS signature support (alternative to DNSSEC)
     "cryptography>=41.0.0",
@@ -86,7 +92,7 @@ all = [
     # MCP
     "mcp>=1.0.0",
     "uvicorn>=0.30.0",
-    # Route53
+    # Backends: Route53, Infoblox, Cloudflare, DDNS (last 3 use core deps)
     "boto3>=1.34.0",
     # JWS
     "cryptography>=41.0.0",