HelpPersistence

Per-node settings wrapper for the help browser (§SPC-6).

Detailed description

Persists through the sanctioned per-node app::Settings (backed by <base-dir>/settings.ini), passed in by HelpActivity from node->settings(). Every write is followed by Settings::flush() so values are durable immediately — the same "don't lose in-flight writes on a quick exit" guarantee the old direct-settings wrapper got from an explicit sync, now provided compliantly (§SPC-2, §PV-D-3).

All keys live under the help/ prefix:

• help/lastPath/path, help/lastPath/anchor, help/lastPath/scrollY
• help/history (string-list, capped to historyCapacity)
• help/treeExpanded (string list)
• help/fontSize, help/splitterState, help/leftSplitterState

The test constructor takes an explicit INI path and builds a dedicated per-instance app::Settings on it, so unit tests stay hermetic (never touching the platform-global store).