feat: Remove checkpoint task types — per-phase review is sufficient

Checkpoint tasks (human-verify, decision, human-action) silently blocked
auto-dispatch with no UI to resolve them. Per-phase review + initiative
review already cover human verification, making checkpoints redundant.

Removed from: schema, dispatch manager, tRPC validators, detail prompt,
frontend types, tests, and docs.

apps/server/agent/prompts/detail.ts

@@ -13,7 +13,7 @@ ${CODEBASE_EXPLORATION}
 
 <output_format>
 Write one file per task to \`.cw/output/tasks/{id}.md\`:
-- Frontmatter: \`title\`, \`category\` (execute|research|discuss|plan|detail|refine|verify|merge|review), \`type\` (auto|checkpoint:human-verify|checkpoint:decision|checkpoint:human-action), \`dependencies\` (list of task IDs that must complete before this task can start)
+- Frontmatter: \`title\`, \`category\` (execute|research|discuss|plan|detail|refine|verify|merge|review), \`dependencies\` (list of task IDs that must complete before this task can start)
 - Body: Detailed task description
 </output_format>
 
@@ -92,14 +92,6 @@ Each task is handled by a separate agent that must load the full codebase contex
 Bundle related changes into one task. "Add user validation" + "Add user API route" + "Add user route tests" is ONE task ("Add user creation endpoint with validation and tests"), not three.
 </task_sizing>
 
-<checkpoint_tasks>
-- \`checkpoint:human-verify\`: Visual changes, migrations, API contracts
-- \`checkpoint:decision\`: Architecture choices affecting multiple phases
-- \`checkpoint:human-action\`: External setup (DNS, credentials, third-party config)
-
-~90% of tasks should be \`auto\`.
-</checkpoint_tasks>
-
 <existing_context>
 - Read ALL \`context/tasks/\` files before generating output
 - Only create tasks for THIS phase (\`phase.md\`)