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/bindings.ts

@@ -0,0 +1,32 @@
+/**
+ * Generate TypeScript bindings from Rust types (ts-rs).
+ *
+ * Usage: bun scripts/bindings.ts
+ */
+
+import { readdirSync, writeFileSync, rmSync } from "fs";
+import { run } from "./lib/proc";
+
+const BINDINGS_DIR = "web/src/lib/bindings";
+
+// Build test binary first (slow part) — fail before deleting anything
+run(["cargo", "test", "--no-run"]);
+
+// Clean slate
+rmSync(BINDINGS_DIR, { recursive: true, force: true });
+
+// Run the export (fast, already compiled)
+run(["cargo", "test", "export_bindings"]);
+
+// Auto-generate index.ts from emitted .ts files
+const types = readdirSync(BINDINGS_DIR)
+  .filter((f) => f.endsWith(".ts") && f !== "index.ts")
+  .map((f) => f.replace(/\.ts$/, ""))
+  .sort();
+
+writeFileSync(
+  `${BINDINGS_DIR}/index.ts`,
+  types.map((t) => `export type { ${t} } from "./${t}";`).join("\n") + "\n",
+);
+
+console.log(`Generated ${BINDINGS_DIR}/index.ts (${types.length} types)`);