feat(mcpd): EpicTask resource — roadmap nodes, edges, and the roadmap view

Roadmap nodes plus the edges that chain them into the dependency graph the
design doc calls the spider web. Edge direction is "from depends on to".

The database cannot enforce graph integrity here — production provisions with
`prisma db push`, so a trigger or CHECK would never exist there, and the schema
test added earlier documents that boundary explicitly. So the service rejects
the three things that would otherwise corrupt the roadmap:

- self-edges,
- edges crossing Epics, since a roadmap is one Epic's graph,
- cycles, which make the graph unschedulable and hang any topological walk.

Cycle detection is a BFS over the prerequisite direction: adding from→to closes
a loop exactly when `to` already depends transitively on `from`. The error names
the offending path, not just "cycle", so a failed apply says which nodes to look
at. The traversal carries a seen-set that also guarantees termination if the
stored graph ALREADY contains a cycle — from a hand-edited database or an
earlier bug — rather than spinning forever. There is a test for that case.

Adding an existing edge is a no-op rather than an error, so applying a manifest
twice is safe.

GET /api/v1/epics/:id/roadmap returns nodes with per-node completeness, both
edge directions, and `ready`: the nodes whose prerequisites are all satisfied,
which is the question anyone actually asks of a roadmap. A cancelled
prerequisite counts as satisfied — it is not coming. Completeness reuses
EpicService.completeness verbatim so a node and its Epic can never disagree
about what "met" means.

Tests: 19 service tests — the full cycle matrix (self, 2-cycle, long transitive,
diamond-is-fine, pre-existing-cycle termination), roadmap edge directions,
readiness including the cancelled-prerequisite case, and CRUD guards.

Local: build clean, workspace 2366 passed (+19), db 128 passed (same 4
pre-existing Secret failures), lint unchanged at 869.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N4wNHWf7xSwnZCWpJcyv9p

.taskmaster/tasks/tasks.json

@@ -2727,9 +2727,9 @@
           "117",
           "123"
         ],
-        "status": "pending",
+        "status": "done",
         "subtasks": [],
-        "updatedAt": "2026-08-08T08:55:58.627Z"
+        "updatedAt": "2026-08-08T10:10:39.751Z"
       },
       {
         "id": "128",
@@ -2741,9 +2741,9 @@
         "dependencies": [
           "127"
         ],
-        "status": "pending",
+        "status": "done",
         "subtasks": [],
-        "updatedAt": "2026-08-08T08:55:58.627Z"
+        "updatedAt": "2026-08-08T10:10:39.761Z"
       },
       {
         "id": "129",
@@ -3251,9 +3251,9 @@
     ],
     "metadata": {
       "version": "1.0.0",
-      "lastModified": "2026-08-08T10:05:28.178Z",
+      "lastModified": "2026-08-08T10:10:39.761Z",
       "taskCount": 162,
-      "completedCount": 111,
+      "completedCount": 113,
       "tags": [
         "master"
       ]