Dynamic responsive masthead menu from documentation manifests #111

Feature Description

Replace current masthead’s fixed Library and current-app breadcrumb-style links with dynamic navigation built from packaged kb-docs.json manifests.

Menu must expose documentation apps and their published HTML pages, allowing package owners to add documentation pages through their manifest without masthead source changes.

Problem / Opportunity

Current masthead only identifies library and active app. Users cannot navigate directly among available documentation sites or pages. Fixed horizontal links also risk overflow on tablet and smaller displays.

Acceptance Criteria

1. Masthead navigation derives app and page entries from loaded kb-docs.json manifests, including manifest-defined page titles, paths, ordering, and sections.
2. Any valid HTML documentation page published in package manifest can appear as clickable navigation item without knowledge-base code changes.
3. Navigation remains usable at every viewport width.
4. Tablet-first responsive behavior prevents horizontal overflow:
   • compact clickable menu control shown when links cannot fit;
   • menu exposes all navigation entries;
   • links wrap or collapse predictably without clipping, overlap, or off-screen content.
5. Menu supports keyboard navigation, visible focus, accessible names, and correct current-page state.
6. Existing catalog and packaged-document navigation paths remain valid.
7. Automated tests cover manifest-driven menu generation, overflow/compact menu behavior, current-page state, and keyboard-accessible controls.

Proposed Solution

Build masthead navigation from normalized manifest data already used during package ingestion. Render full navigation when space allows; use accessible collapsible/disclosure menu at tablet-sized and narrower layouts, or when measured links overflow.

Keep catalog entry available and preserve absolute knowledge-base URL behavior.

Dependencies / Related

None.

Additional Context

Current artifact contract already supports per-app page metadata: titles, paths, ordering, and optional sections. Existing masthead currently renders library plus active-app context only.