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/Integration.hs

@@ -0,0 +1,23 @@
+module Main where
+
+import Test.Hspec
+import IHP.Prelude
+import IHP.ModelSupport
+import IHP.Log.Types
+import System.Environment (lookupEnv)
+
+-- Integration tests run with a temporary PostgreSQL database.
+-- The DATABASE_URL env var is set automatically by `nix flake check`.
+-- See: https://ihp.digitallyinduced.com/Guide/testing.html
+main :: IO ()
+main = do
+    databaseUrl <- lookupEnv "DATABASE_URL" >>= \case
+        Just url -> pure (cs url)
+        Nothing -> error "DATABASE_URL not set. Run `devenv up` first or use `nix flake check`."
+    logger <- newLogger def { level = Warn }
+    withModelContext databaseUrl logger \modelContext -> do
+        let ?modelContext = modelContext
+        hspec do
+            describe "Database" do
+                it "can execute a query" do
+                    sqlExecDiscardResult "SELECT 1" ()