The data layer for per-item workflow prompts shipped in `Task-add-workflow-prompt-to-backlog-items`. This task adds the UI surface that uses it.
Deferred from the parent task because `apps/web` does not yet have a backlog-item detail panel — `apps/web/components/panels/object-detail.tsx` is for the `objects` table, not `markdown_backlog_items`. Adding a new panel surface (state, edit affordance, draft handling) is a substantive UI task on its own.
## Description
Add a "Workflow prompt" section to wherever a single backlog item is rendered for read/edit. Likely surfaces:
1. A dedicated route like `/[workspaceSlug]/plans/[planSlug]/[epicSlug]/[taskSlug]` if a Plans browser ever exists.
2. A drawer or sheet opened from the Plans tree (if/when that ships).
3. The agent runs view (`/settings/runs`) — click a run to expand task context including the effective prompt.
For v1 of THIS task, pick the smallest surface that lets an operator actually use the data:
- **Effective prompt** — read-only display from `api.backlog.getWorkflowPrompt({ backlogItemId })`. Show the source level as a small badge ("From this task" / "Inherited from epic: X" / "Inherited from plan: Y" / "Built-in default").
- **Override** — a textarea bound to `ownOverride`. Empty = inherit. Save calls `api.backlog.updateWorkflowPrompt`.
- [x] Decide on the rendering surface (see options above).
- [x] Build the section component with effective-prompt preview + override textarea.
- [x] Owner/admin gate matches the procedure (the procedure refuses non-managers, but the UI should hide the save button rather than let the click fail).
- [x] Show "clear override" affordance when an override is set.
- [x] Saving an override flips the source badge to "From this task."
- [x] Clearing an override re-shows the inherited source.
- [x] Non-managers see the prompt but cannot edit it.
## Implementation notes
- Surface picked: dedicated route at `/[workspaceSlug]/plans/[planSlug]/[epicSlug]/[taskSlug]`. There's no plans-tree browser yet — this lets an operator land on a task by typing the URL (or future deep-link from `/settings/runs`) without first shipping a tree view.
- New tRPC procedure: `backlog.getTaskByPath({ planSlug, epicSlug, taskSlug })` — returns task row, parent epic + plan titles (for inheritance badge), and `callerRole` so the UI can pre-hide edit affordances in a single roundtrip. Slugs are re-validated against the importer's `[a-z0-9-]` shape at the procedure boundary.
- New component: `components/backlog/workflow-prompt-section.tsx`. Source badge derives its label from `(source, sourceContext)`; preview is read-only `<pre>`; textarea is the editable knob bound to `ownOverride`. Save calls `backlog.updateWorkflowPrompt`; Clear sends `workflowPrompt: null`. Both invalidate `getWorkflowPrompt` rather than optimistic-mutate, because clearing a task override can re-expose an epic/plan inheritance the client doesn't know about ahead of time.
- Server still gates writes via `ctx.workspace.role`; the UI hide is convenience, not security.
## Follow-ups
- Linking from `/settings/runs` rows to the task detail page (needs `planSlug`/`epicSlug`/`slug` on `runs.listRecent`).
- Plans tree browser at `/[workspaceSlug]/plans` (currently only the leaf route exists).
