feat(nav): one canonical RepoNav — data-derived keys, insights sub-nav unified, lost pages find their way home #5550

Queue item: the flow audit's navigation-coherence findings (#4, #7 and the active-key list), built to the ADMIN_NAV standard.

• RepoNav rebuilt on canonical exported data arrays (REPO_NAV_PRIMARY / REPO_NAV_AI_GROUPS / REPO_NAV_MORE / REPO_NAV_SETTINGS); the RepoNavKey union is derived from the arrays, so the type and the rendered menus agree by construction — the two dead union members are gone and the nine menu destinations that could never highlight now can.
• Insights sub-nav unified: one InsightsSubNav component replaces seven mutually inconsistent hand-rolled strips (dora.tsx, which had NO sub-nav and was a terminal node, gets one too). All seven destinations reachable from every insights page, tokens only.
• Wrong active= fixed across the AI pages (which were funneling through IssueNav's 3-key type), contributors, docs-tracking, previews. (packages.tsx was already correct — the audit's claim didn't survive verification.)
• Navigation restored on deployments (both pages), wiki home, ask, claude-web, dev-env (all four page states), fork — the last four previously rendered no repo identity at all.
• aria-current="page" at every RepoNav render site, matching SettingsNav.
• A regression guard that can't lie: repo-nav-coherence.test.ts (26 tests) renders RepoNav from the exported data for every key and asserts exactly one aria-current anchor with the canonical href — data-driven both directions, unlike the source-string guards that passed while these defects persisted.

Deliberately scoped out (follow-up): deployments' two detail sub-pages and wikis' six sub-pages.

Verified on current main after cherry-pick: typecheck clean; repo-nav-coherence + nav-tab-fixes + orphan-links + adjacent suites 48 pass locally, full suite in CI.