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>

dashboard/src/docs/tasks.md

@@ -0,0 +1,95 @@
+---
+title: Tasks — Reference
+---
+
+# Tasks — Reference
+
+The Tasks page shows all tasks across every workstream and domain, with live
+filtering, a status distribution chart, and a blocked-tasks highlight section.
+
+---
+
+## Task statuses
+
+| Status | Meaning |
+|--------|---------|
+| **todo** | Not yet started |
+| **in_progress** | Actively being worked on |
+| **blocked** | Cannot proceed — has a blocking reason |
+| **done** | Completed |
+| **cancelled** | Dropped; not counted toward totals |
+
+---
+
+## Task priorities
+
+| Priority | Use for |
+|----------|---------|
+| **critical** | Must be resolved immediately; blocks a release or governance gate |
+| **high** | Should be resolved this session or next |
+| **medium** | Normal backlog priority |
+| **low** | Nice-to-have; deferred is acceptable |
+
+---
+
+## Filter bar
+
+| Filter | Effect |
+|--------|--------|
+| **Status** | Multi-select — show only chosen statuses |
+| **Priority** | Multi-select — show only chosen priorities |
+| **Domain** | Multi-select — filter by domain slug |
+| **Assignee** | Case-insensitive substring match on the assignee field |
+
+All filters are applied client-side after each poll.
+
+---
+
+## Status Distribution chart
+
+A horizontal bar chart (Observable Plot) showing the count of filtered tasks
+per status, colour-coded:
+
+| Colour | Status |
+|--------|--------|
+| grey-blue | todo |
+| blue | in_progress |
+| red | blocked |
+| green | done |
+| light grey | cancelled |
+
+---
+
+## Blocked Tasks section
+
+Shows cards for every task currently in `blocked` status within the active
+filter. Each card displays:
+
+- Priority badge and status
+- Domain and workstream context
+- Task title
+- Blocking reason (amber background)
+
+---
+
+## KPI sidebar card
+
+Shows four counts for the unfiltered dataset: open (todo + in_progress +
+blocked), blocked, in progress, done, and a done-% of total.
+
+---
+
+## Sorting
+
+Tasks are sorted by status (blocked first, then in_progress, todo, done,
+cancelled) then by priority (critical → high → medium → low) within each
+status group.
+
+---
+
+## Data sources
+
+Polls every **15 seconds**:
+- `GET /tasks/?limit=500`
+- `GET /workstreams/`
+- `GET /topics/`