C4: Replace /work and /work-item templates with preview design

[nextlevelshit]

Parent

Epic #1624
Depends on: #1627 (C1)

Scope

Replace /work (board) and /work-item (detail) templates with preview mockup designs. These are the largest templates — the work board is the main dispatch surface.

Current state

• templates/work/board.html — already uses Tailwind (standalone, no layout.html), shows bindings table + recent matches
• templates/work/detail.html — may use layout or Tailwind, shows work item detail with pipeline dispatch
• Handlers: handlers_work.go serves WorkBoard and WorkItemDetail data

Target state

• New templates/work/board.html — preview design
  • Top nav from C1 (Work active)
  • Page header: "Work" + Refresh + New work buttons
  • Filter bar: forge, kind, status, label, search
  • List rows with: icon (issue/PR/scheduled), title, meta (forge, age, author, tags), kind badge, status badge, action button (Run/View)
  • Pagination footer
  • Bindings section preserved (table of configured worksource bindings)
• New templates/work/detail.html — preview design
  • Breadcrumb: Work > Forge/Repo > Issue #N
  • Page header: title + status badge + labels + external link
  • Split layout: left = issue body + pipeline bindings + recent runs, right = item metadata + cost forecast
  • Pipeline dispatch: radio buttons for bound pipelines, custom pipeline expandable section
  • Run/Run now buttons

Acceptance criteria

• /work renders with preview design (nav, filter bar, list rows)
• /work/{id} renders with preview design (breadcrumb, split layout, dispatch)
• Filter/search controls work
• Pipeline dispatch buttons still POST to correct endpoints
• External forge link opens correctly
• Visual smoke in chromium: both pages render correctly

Files touched

• internal/webui/templates/work/board.html (rewrite)
• internal/webui/templates/work/detail.html (rewrite)
• internal/webui/handlers_work.go (possibly minor — template data mapping)

[nextlevelshit]

Blocked by #1627

[nextlevelshit]

Covered by PR #1633 (C3) — work pages migrated to unified design system alongside onboard and proposals.