fix: pass GIT_SHA inline to npm run build

The export-then-chain wasn't propagating into the subshell.
Use Make variable and pass GIT_SHA= directly to the command.

Makefile

@@ -1,6 +1,8 @@
 SHELL := /bin/bash
 .PHONY: build build-web build-server build-tui run run-tui dev docker-up docker-down clean
 
+GIT_SHA := $(shell git rev-parse --short HEAD)
+
 # Build everything
 build: build-web build-server
 
@@ -18,7 +20,7 @@ docs:
 
 # Build the web frontend
 build-web:
-	cd web && export GIT_SHA=$$(git rev-parse --short HEAD) && ([ -s ~/.nvm/nvm.sh ] && . ~/.nvm/nvm.sh && npm run build || npm run build)
+	cd web && ([ -s ~/.nvm/nvm.sh ] && . ~/.nvm/nvm.sh && GIT_SHA=$(GIT_SHA) npm run build || GIT_SHA=$(GIT_SHA) npm run build)
 
 # Run the server locally (dev mode)
 run: build-server