Task: Consolidate site top navigation

An external (Gemini) UX review of the redesigned homepage flagged the site-wide top nav's four dropdowns (Project, Modeling, Developer, Resources) as fragmenting the user journey. Group developer technical specs and model definitions under a single unified Docs dropdown, reducing the top-level dropdown count. This is a site-wide change (every page's site-html-preamble in ores-build-site.el, not just index.org), so it needs its own careful pass over what's currently in each dropdown before restructuring.

• Nav dropdown count reduced (fewer than the current 4 top-level groups), with developer technical specs and model definitions consolidated under one Docs-style grouping.
• Every existing nav link still resolves correctly on every page (the preamble is injected site-wide, so a broken link here breaks every page, not just one).
• No regression in the site build (compass build --direct site clean, no broken id-links).

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

Manual QA scenarios (scaffolded via compass add test_scenario, run through the QA Validation Runner panel) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.