chore(deno): finish import extensions for sites/mp-sync paths

- sites/mp-sync relative imports already carry extensions; drop the biome
  useImportExtensions override and --unstable-sloppy-imports in typecheck:deno
- mp-sync scripts: deno shebang (+x), static `import YAML from "yaml"`,
  README/usage switched to `deno run -A`
- verified: check.mjs --to e6820a8 (49 unchanged), movieclaw-import --check (0 diff)

Co-Authored-By: Claude Fable 5.1 <[email protected]>

scripts/mp-sync/lib.mjs

@@ -1,4 +1,4 @@
-// mp-sync 公共函数(Node 24 / Deno 2 均可运行,无第三方依赖)
+// mp-sync 公共函数(Deno 2 运行,无第三方依赖)
 import { execFileSync } from "node:child_process";
 import { createHash } from "node:crypto";
 import { existsSync, readdirSync, readFileSync, statSync } from "node:fs";