feat: gate the plugin's own diagnostics behind a log level

[osmaczko]

Every diagnostic the plugin printed went to stderr unconditionally, and two of them fire on every delivery event the node emits, so an embedding host took a per-event line plus a dump of the full event payload, message contents included, into its console and its log files.

Verbosity now follows createNode's logLevel, shared with the node's own logger, with DELIVERY_MODULE_LOG_LEVEL overriding it for the plugin's own lines and covering the ones printed before a configuration arrives. Each line carries the token the host's stderr classifier keys on, so a forwarded line is logged at its real severity rather than always at info.

Scope: the module's own diagnostics. The embedded node logs separately, to stdout, and this change does not affect it, so it does not on its own quiet the console output reported in logos-co/logos-chat-ui#37 — the lines there are the node's. Making the node honor logLevel is a fix in logos-delivery's nix build, tracked separately.

[github-actions]

📊 delivery-module doc-test report

This commit of the delivery module, packaged as an .lgx and run through a logoscore daemon — rendered alongside the commands actually run and their output (updated each run, commit 23922fc):

• ubuntu-latest report
• macos-latest report

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