♻️ Surface settings errors with typed codes and paths

[Gudsfile]

Summary

Refs #169

• Settings errors now carry a machine-readable code and the path of the affected setting, so there is a reliable way to inspect what failed without parsing error strings.
• The CLI uses these fields to build user-facing messages, replacing brittle string matching on error text.
• Pydantic validation failures are rendered using the structured errors API rather than a custom text parser.
• Migration errors (invalid JSON root structure) now also carry the file path — previously lost before reaching the CLI renderer.

Test plan

• Run jukebox-admin settings set <unsupported.path> value and verify the error message names the path.
• Set a setting to an invalid JSON value and verify the message distinguishes between a parse failure and a wrong type.
• Trigger a Pydantic validation failure (e.g. set a port to a string) and verify the field name and constraint appear in the output.
• Run with --verbose and verify full details are still visible.
• Write a settings file whose JSON root is an array (e.g. [1,2,3]) and verify the error message includes the file path.

[Gudsfile]

uv run jukebox-admin settings set jukebox.reader.pn532.spi.cs.toto 12

Unsupported settings path: 'jukebox.reader.pn532.spi.cs.toto'. Use `jukebox-admin settings show --effective --json` to inspect supported editable paths.

---

extra ,

Malformed settings file at '/Users/username/.config/jukebox/settings.json'. Fix the JSON syntax and try again.

---

"jukebox": { "reader": { "type": "toto" } }

Persisted settings are invalid at '/Users/username/.config/jukebox/settings.json': jukebox.reader.type: Input should be 'dryrun' or 'pn532'

---

uv run jukebox-admin settings set admin.api.port toto

Settings update rejected: admin.api.port: Input should be a valid integer, unable to parse string as an integer

---

"admin": { "api": { "port": -1 } }

Persisted settings are invalid at '/Users/username/.config/jukebox/settings.json': admin.api.port: Input should be a valid integer, unable to parse string as an integer

---

"admin": { "api": { "port": -1 } } + --verbose

Persisted settings are invalid at '/Users/username/.config/jukebox/settings.json': admin.api.port: Input should be greater than or equal to 1

Details: Invalid settings file at '/Users/username/.config/jukebox/settings.json': 1 validation error for PersistedAppSettings
admin.api.port
  Input should be greater than or equal to 1 [type=greater_than_equal, input_value=-12, input_type=int]
    For further information visit https://errors.pydantic.dev/2.13/v/greater_than_equal