Support scripts section in entity manifest for manifest-defined ScriptEntryConfig

[bburda]

Summary

DefaultScriptProvider supports manifest-defined scripts via ScriptsConfig.entries, but there is no way to populate these entries from configuration. The entries vector is always empty unless populated programmatically in C++.

The entity manifest (sensor_manifest.yaml, turtlebot3_manifest.yaml, etc.) already defines the full entity hierarchy (areas, components, apps, functions) via ManifestParser. Scripts should be loadable from the same manifest file as a new top-level section.

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Proposed solution

Extend the entity manifest YAML with an optional scripts: section:

# In sensor_manifest.yaml (alongside existing areas/components/apps/functions)
scripts:
  - id: "run-diagnostics"
    name: "Run Diagnostics"
    description: "Check health of all sensors"
    path: "/opt/scripts/run-diagnostics.sh"
    format: "bash"
    timeout_sec: 30
    entity_filter: ["compute-unit"]
    env:
      GATEWAY_URL: "http://localhost:8080"
  - id: "inject-nan"
    name: "Inject NaN Fault"
    description: "Enable NaN values on all sensors"
    path: "/opt/scripts/inject-nan.sh"
    format: "bash"
    timeout_sec: 30
    entity_filter: ["compute-unit"]

Implementation scope:

1. Add parse_scripts() to ManifestParser - parse scripts: section into std::vector<ScriptEntryConfig>
2. Extend Manifest struct with scripts field
3. In gateway_node.cpp, after manifest parsing, populate scripts_config.entries from manifest.scripts
4. Scripts loaded from manifest are managed: true (immutable, not deletable via API)
5. Unit tests for script manifest parsing
6. Update manifest documentation with scripts section reference

This follows the existing pattern - ManifestParser already uses yaml-cpp and parses Areas/Components/Apps/Functions. Adding scripts is a natural extension.

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Additional context

Needed for selfpatch/selfpatch_demos#42 (Scripts API demo integration). All three demos need manifest-defined scripts to showcase the Scripts API feature.

Currently ScriptsConfig.entries fields per entry: id, name, description, path, format, timeout_sec, entity_filter (string vector), env (string map), args (JSON array), parameters_schema (optional JSON).