Set the GH_REPO environment variable in session startup (#17774)

Otherwise, `gh` fails because it cannot determine what the target
repository is.

Co-authored-by: Claude <noreply@anthropic.com>

.claude/hooks/session-start-web.sh

@@ -9,3 +9,8 @@ fi
 
 # Install clippy and rustfmt for the active toolchain.
 rustup component add clippy rustfmt
+
+# Set GH_REPO so `gh` works even when the git remote points to a local proxy
+if [ -n "${CLAUDE_ENV_FILE:-}" ]; then
+  echo 'export GH_REPO=astral-sh/uv' >> "$CLAUDE_ENV_FILE"
+fi