feat(runtime): add effective plugin config helpers

[offendingcommit]

Summary

• add load_plugin_config for current Hermes hosts whose PluginManifest does not carry runtime profile config
• preserve manifest.config as an older-host and test compatibility seam
• add operator-gated, idempotent stderr logging for plugin registration receipts
• document and test both shared APIs

Root cause

Configurable plugins that read only ctx.manifest.config silently fell back to defaults on current Hermes. This left memory-sync enabled but without its authored-memory lifecycle tools, hooks, or slash commands.

Validation

• 69 unittest tests passed
• Python compileall passed
• git diff --check passed