feat(T01): bootstrap IHP v1.5 project scaffold

Merged ihp-new generated scaffold into repo. Sets appName to inter-hub,
adds Nix flake with IHP inputs, devenv config, and standard IHP project
structure. Nix + ihp-new + direnv installed system-wide.

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

Config/Config.hs

@@ -0,0 +1,11 @@
+module Config where
+
+import IHP.Prelude
+import IHP.Environment
+import IHP.FrameworkConfig
+
+config :: ConfigBuilder
+config = do
+    -- See https://ihp.digitallyinduced.com/Guide/config.html
+    -- for what you can do here
+    pure ()