feat: add web UI prompt library from canonical workflows (#428)

Surface short copy/paste operator prompts derived from canonical workflow
files with workflow path and SHA-256 citations. Adds /prompts, /prompts/{id},
and /api/prompts with one-click copy.

Closes #428

webui/prompt_library.py

@@ -128,7 +128,7 @@ def load_prompt_library() -> tuple[PromptEntry, ...]:
         ),
         _static_entry(
             slug="comment-issue",
-            label="Comment issue",
+            label="Comment on issue",
             workflow_path=str(_WORKFLOW_ROOT / "create-issue.md"),
             prompt_text=(
                 "Comment on the target Gitea issue only if exact comment_issue "
@@ -140,16 +140,14 @@ def load_prompt_library() -> tuple[PromptEntry, ...]:
         ),
         _static_entry(
             slug="cleanup",
-            label="PR queue cleanup",
-            workflow_path=str(_WORKFLOW_ROOT / "pr-queue-cleanup.md"),
+            label="Post-merge cleanup",
+            workflow_path="skills/llm-project-workflow/templates/worktree-cleanup.md",
             prompt_text=(
-                "Run PR-only queue cleanup: build a complete open-PR inventory "
-                "with pagination proof, select exactly one eligible PR, dispatch "
-                "one canonical review for that PR, then stop after any terminal "
-                "review mutation. Load pr-queue-cleanup.md and review-merge-pr.md "
-                "before any mutation."
+                "Task: clean up branch/worktree for PR #<pr> / issue #<n> after merge. "
+                "Confirm the merge on remote master before any deletion; never "
+                "force-remove a dirty worktree."
             ),
-            source_note="Derived from pr-queue-cleanup.md; composes with review-merge-pr.md.",
+            source_note="Full cleanup steps live in templates/worktree-cleanup.md.",
         ),
         _entry_from_workflow(
             slug="audit",
@@ -159,19 +157,26 @@ def load_prompt_library() -> tuple[PromptEntry, ...]:
         _static_entry(
             slug="onboarding",
             label="Project onboarding",
-            workflow_path="docs/webui-local-dev.md",
+            workflow_path="skills/llm-project-workflow/SKILL.md",
             prompt_text=(
-                "Start a new MCP Control Plane session: call mcp_get_control_plane_guide, "
-                "prove identity and task capability, then complete the onboarding checklist "
-                "for this project at /projects. Keep Gitea, MCP tools, and canonical "
-                "workflows as the source of truth."
+                "Onboard this repository into the MCP Control Plane: prove identity "
+                "and task capability, configure author/reviewer/reconciler profiles "
+                "in separate namespaces, then complete the checklist at /projects. "
+                "Canonical router: skills/llm-project-workflow/SKILL.md."
             ),
-            source_note="Operator onboarding; checklist details live in the project registry UI.",
+            source_note="Checklist details live in webui/data/projects.registry.json and /projects.",
         ),
     )
     return entries
 
 
+def find_prompt(slug: str) -> PromptEntry | None:
+    for entry in load_prompt_library():
+        if entry.slug == slug:
+            return entry
+    return None
+
+
 def prompt_to_dict(entry: PromptEntry) -> dict[str, Any]:
     return {
         "slug": entry.slug,