feat(dashboard): nav restructure, full context-help coverage, 11 new ref docs

Navigation:
- New order: Overview · Todo · Domains · Repos · Workstreams (collapsible,
  open:false, with atomic sub-entries: Decisions, Tasks, Debt, Extends,
  Dependencies) · Contributions · SBOM · Progress · Reference (collapsible)
- Reference section gains path:/reference landing page; all 18 doc pages
  listed in nav (alphabetical) and in reference.md table

New pages:
- todo.md — Internal / Ecosystem / Third-party todo classification
- dependencies.md — dependency edge table derived from state/summary
- reference.md — Reference landing page with full doc index

New reference doc pages (11):
  contributions, debt, dependencies, domains, extensions, overview,
  repos, tasks, todo + reference (meta) already added previously

doc-overlay.js — lazy bubblehelp tooltip:
- _titleCache Map + _fetchDocTitle(docPath): on first hover of any ?
  button, fetches the target doc page, parses <h1>, sets btn.title
- Native browser tooltip appears exactly on the ? circle on subsequent hover

Context-help wired on all 14 dashboard pages:
- h1 withDocHelp added to: index, todo, domains, repos, tasks, techdept,
  extensions, dependencies (contributions/workstreams/decisions/sbom/
  progress/reference were already wired)
- domains.md + repos.md: added missing withDocHelp import and live-data link
- tasks/techdept/extensions: removed duplicate _h1 const that caused
  SyntaxError: Identifier '_h1' has already been declared

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

state-hub/dashboard/src/reference.md

@@ -0,0 +1,47 @@
+---
+title: Reference
+---
+
+```js
+import {withDocHelp} from "./components/doc-overlay.js";
+
+const _h1 = document.querySelector("#observablehq-main h1");
+if (_h1) { _h1.style.position = "relative"; withDocHelp(_h1, "/docs/reference"); }
+```
+
+# Reference
+
+In-depth documentation for each dashboard page, data model, and design
+convention used in the Custodian State Hub.
+
+---
+
+## Dashboard pages
+
+| Page | What it covers |
+|------|---------------|
+| [Contributions](/docs/contributions) | Contribution types, lifecycle, third-party todo workflow |
+| [Decision Health](/docs/decisions-kpi) | KPI formula, avg resolve time, open-age colour thresholds |
+| [Decisions](/docs/decisions) | Decision types, statuses, escalation rules, filter bar |
+| [Dependencies](/docs/dependencies) | Dependency edges, registration, cycle detection |
+| [Domains](/docs/domains) | Domain model, statuses, cards with repos |
+| [Extension Points](/docs/extensions) | EP types, statuses, priorities, registration |
+| [Inter-Repo Communication](/docs/inter-repo-communication) | Boundary rule, Internal/Ecosystem/Third-party taxonomy, routing workflows |
+| [Live Data](/docs/live-data) | Poll interval, live indicator states, offline recovery |
+| [Overview](/docs/overview) | State summary sections, workstream chart, blocking decisions, next steps |
+| [Progress Log](/docs/progress-log) | Event types, append-only policy, session protocol |
+| [Repos](/docs/repos) | Repo registry, SBOM coverage map, ingestion commands |
+| [SBOM](/docs/sbom) | Lockfile ingestion, licence report, copyleft detection |
+| [Tasks](/docs/tasks) | Task statuses, priorities, filter bar, status distribution chart |
+| [Technical Debt](/docs/debt) | Debt types, severities, statuses, registration |
+| [Todo](/docs/todo) | Internal/Ecosystem/Third-party classification, data sources |
+| [Workstream Health](/docs/workstream-health-index) | WHI formula, six base metrics, per-domain breakdown |
+| [Workstreams](/docs/workstreams) | Workstream statuses, dependency edges, WHI KPI card |
+
+---
+
+## Meta
+
+| Topic | What it covers |
+|-------|---------------|
+| [Reference & Context Help](/docs/reference) | How reference pages work; the ? context-help button |