Add machine-readable project, template, and service discovery

[delaudio]

Parent epic: #31

Problem

An integration cannot build a project/template picker without reading Hum's private registry format or parsing configuration files itself.

Scope

Add supported structured commands for:

• listing registered projects;
• inspecting one registered project;
• enumerating its templates and services;
• exposing safe presentation metadata such as configured port, URL, runtime kind, and dependency names.

Suggested command shapes:

hum project list --json
hum project inspect <name> --json

The final CLI shape may differ, but discovery must not require a template name that has not yet been discovered.

Acceptance criteria

• Registered projects can be listed in one JSON response.
• A project can be inspected without reading the registry or YAML externally.
• Templates and their root services are included.
• Services include only non-secret metadata suitable for display.
• Missing or invalid registrations use the common structured error envelope.
• Relative config paths are resolved consistently with normal Hum commands.
• Contract fixtures cover empty registries, valid projects, invalid configs, and unknown projects.
• Human-readable project management behavior remains compatible.