HeaderBar

The plain, Node-free navigation header — §ACW-7.1's first extraction.

In the namespace octomy::header. Declared in src/libs/libheader/header/HeaderBar.hpp.

Detailed description

`NodeNavigation` is the chrome slice of the `NodeWindow` god-object: it implements `ActivityHeader`, but it is welded to `Node` (Hive, swarm badges, the identity chip), so a standalone app could not get "a title that follows the current activity and a back button that pops the stack" without dragging `Node` in. This class is the seam's base widget: the same interface, none of the coupling.

The shape is a LIBRARY, not a framework (owner decision 2026-09-10, patterned on construct's toolbar slot):

- **The app owns placement.** This is a plain `QWidget`. Mount it on a `QToolBar` slot, a top-of-window widget, or anywhere else; nothing here assumes an overlay or a layout. - **The app owns content.** The base carries back / title / menu. Extra affordances are addSegment widgets the app chooses — the same each-user-stuffs-its-own-bar model as `StandaloneCompatBar`. Node chrome (identity chip, swarm badge) stays in `NodeNavigation`, which becomes one USER of this seam rather than the seam itself. - **The stack wiring lives elsewhere.** `ActivityStack` already drives any `ActivityHeader` (title follows the active activity, back is relayed after up-target handling); the standalone glue that connects the two is `octomy::window::WindowHeaderHost`, not this class.

Note: §ACF-5 classification: a plain widget, not GLUE and not a `Service` — it has no host, no lifecycle tier and no wiring of its own. That is what makes it adoptable from every side of the window axis.