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>

Test/Main.hs

@@ -0,0 +1,13 @@
+module Main where
+
+import Test.Hspec
+import IHP.Prelude
+
+-- Import your test specs here:
+-- import Test.MySpec
+
+main :: IO ()
+main = hspec do
+    describe "Example" do
+        it "should pass" do
+            1 + 1 `shouldBe` (2 :: Int)