feat(infoview): add history navigation and sectioned display

[epjnre]

• History: [H / ]H to go back/forward through previous goal states (max 30 per pin).
• Sectioned display: optional headers (── Goals ──, etc.). Enabled by setting sectioned_display = true in view options.
• New view option: sectioned_display (boolean).

Changes:

• Pin stores history and history_index; adds history_back() / history_forward().
• Pin:update() saves current element to history on successful commit.
• wrap_sectioned_content, contents_for_interactive_sectioned for sectioned rendering.
• Infoview:render_contents() dispatches to sectioned renderer when enabled.
• Keymaps for [H / ]H in __setup_pin_keymaps.
• Module exports: history_back, history_forward, toggle_sectioned_display.