refactor: extract Justfile inline scripts into scripts/ directory

Move all [script("bun")] blocks into standalone TypeScript files under
scripts/ with shared utilities in scripts/lib/. The Justfile is now ~40
lines of thin `bun scripts/*.ts` wrappers.

Shared code consolidated into two lib files:
- lib/proc.ts: process spawning (run, spawnCollect, raceInOrder, ProcessGroup)
- lib/fmt.ts: color output, elapsed timers, reusable flag parser

scripts/tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "target": "ESNext",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "noEmit": true,
+    "skipLibCheck": true,
+    "types": ["bun-types"],
+    "paths": {
+      "#lib/*": ["./lib/*"]
+    }
+  },
+  "include": ["**/*.ts"]
+}