Friendlier YAML parse errors when working/*.yaml is malformed

[samson-ailabs]

Currently scripts/lib/schema.mjs loads YAML with no error handling:

function loadYaml(path) {
  return yaml.load(readFileSync(path, "utf8"));
}

When working/profile.yaml or working/criteria.yaml is malformed (a stray tab, bad indentation, missing colon), the user gets a raw YAMLException from js-yaml with no file context — just something like bad indentation of a mapping entry at line 25, column 5. They have to guess which file broke.

Task: wrap loadYaml() in scripts/lib/schema.mjs to catch YAMLException and re-throw with file-aware context. js-yaml's YAMLException exposes .mark with line, column, and name properties — use these to build a friendly message.

Expected message shape:

Couldn't parse working/profile.yaml — bad indentation at line 25, column 5.
Check the YAML syntax around that line.

Acceptance:

• Intentionally break working/profile.yaml (add a stray tab, drop a colon, etc.)
• Run any script that loads YAML (e.g. via /argopia-survey)
• User sees a friendly message naming the file and the offending line/column — not a raw stack trace
• All other call sites of loadYaml() benefit automatically (it's the single chokepoint)

Scope: scripts/lib/schema.mjs is the only file that needs changing. No new dependencies.