refactor: remove legacy mkOpencodeRules alias and opencode-rules compat entry

- Remove mkOpencodeRules backward-compat alias from lib/coding-rules.nix
- Remove opencode-rules alias from lib/default.nix
- Update shells/opencode.nix to use mkCodingRules / coding-rules
- Remove backward-compat test from tests/lib/coding-rules-test.nix
- Update AGENTS.md and modules/home-manager/AGENTS.md docs
- Apply nix fmt formatting to shared-options.nix

shells/opencode.nix

@@ -1,5 +1,5 @@
 # OpenCode development environment with AI coding rules
-# This shell demonstrates the mkOpencodeRules library provided by this repository
+# This shell demonstrates the mkCodingRules library provided by this repository
 # Usage: nix develop .#opencode
 #
 # To enable OpenCode rules, add the agents input to your flake:
@@ -13,16 +13,16 @@
   inputs ? null,
   agents ? null,
 }: let
-  # Import the opencode-rules library
+  # Import the coding-rules library
   m3taLib = import ../lib {lib = pkgs.lib;};
 
   # Import custom packages
   customPackages = import ../pkgs {inherit pkgs inputs;};
 
   # Create rules configuration only if agents input is provided
-  # This demonstrates how to use mkOpencodeRules in a real project
+  # This demonstrates how to use mkCodingRules in a real project
   rulesConfig = lib.optionalAttrs (agents != null) {
-    rules = m3taLib.opencode-rules.mkOpencodeRules {
+    rules = m3taLib.coding-rules.mkCodingRules {
       # Pass the AGENTS repository path
       inherit agents;
 
@@ -75,7 +75,7 @@ in
     shellHook = ''
       echo "🤖 OpenCode Development Environment"
       echo ""
-      echo "This environment demonstrates the mkOpencodeRules library"
+      echo "This environment demonstrates the mkCodingRules library"
       echo "provided by the m3ta-nixpkgs repository."
       echo ""
 
@@ -121,7 +121,7 @@ in
       ${
         if (agents == null)
         then ''
-          echo "💡 Using mkOpencodeRules in your project:"
+          echo "💡 Using mkCodingRules in your project:"
           echo ""
           echo "Add to your flake.nix:"
           echo "  inputs = {"
@@ -137,7 +137,7 @@ in
           echo "      system = \"x86_64-linux\";"
           echo "      pkgs = nixpkgs.legacyPackages.''${system};"
           echo "      m3taLib = m3ta-nixpkgs.lib.''${system};"
-          echo "      rules = m3taLib.opencode-rules.mkOpencodeRules {"
+          echo "      rules = m3taLib.coding-rules.mkCodingRules {
           echo "        inherit agents;"
           echo "        languages = [\"python\" \"typescript\"];"
           echo "        frameworks = [\"n8n\"];"