feat(mcp): S5 — issue-kind guidance across all instruction surfaces

Plan #825 (T2 — Issues task_kind) shipped S1–S4 but its S5 docs slice
never landed, so every behavioral surface the plugin pushes to the agent
still described the pre-kind convention ("tag `issue`" on a create_note).
Result: agents fixed bugs without reaching for kind=issue and dumped the
work as logs on unrelated open tasks.

- _INSTRUCTIONS: rewrite the "record a problem" bullet to
  create_task(kind="issue") with symptom→cause→fix + arose_from_id /
  system_ids, and an explicit "not a work-log on an unrelated task"; add
  Issue + System to the hierarchy section.
- skills/systematic-debugging, verification: drop "tag `issue`" /
  create_note-issue, point at create_task(kind="issue").
- skills/using-scribe: add issues/systems to the entity list + reflex #6.
- hooks/scribe_static_context: fix → its own issue on the keyless floor.

Instance-agnostic, prose-only; no schema or tool-behavior change.
Pairs with always-on rule #118. Issue: #855.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/scribe/mcp/server.py

@@ -24,6 +24,12 @@ What each part is for, and when to reach for it:
   todo/in_progress/done/cancelled, optional priority). A task is a note with a
   status — reach for one when there is something to DO. Record progress over
   time with work-logs (add_task_log) rather than rewriting the body.
+- Issue: a task whose kind is corrective — a problem you fixed or are fixing, as
+  opposed to productive `work`. Create it with create_task(kind="issue"); the
+  body carries symptom → root cause → fix. It has the full task lifecycle, and
+  can link the originating task it arose from (arose_from_id) and the System(s)
+  it touches (system_ids). Reach for one whenever you fix something — even in
+  passing — instead of burying the fix in another task's work-log.
 - Plan: a MILESTONE acting as a plan container — HOW you'll execute a chunk of
   work. The design/intent lives in the milestone `body`; each step is its own
   child task (create_task(milestone_id=...)), tracked with status + work-logs —
@@ -35,6 +41,10 @@ What each part is for, and when to reach for it:
 - Note: durable free-form knowledge — reference material, decisions, logs of
   what happened.
   No lifecycle, not actionable. Reach for one to CAPTURE something worth keeping.
+- System: a per-project, reusable, self-describing subsystem/area. Associate any
+  record (note, task, issue) with it via system_ids so research, build-work, and
+  fixes for the same area line up, and recurring problem-spots surface. Manage
+  with create_system / list_systems / get_system.
 - Typed entities (person/place/list): structured records about people, places,
   and checklists.
 
@@ -90,9 +100,13 @@ Keep task state honest — this is what makes the project a trustworthy record:
   that changes direction — write a short dated note on the project (create_note)
   capturing what happened (the pivots, not just the wins), and set the finished
   task to done.
-- When you record a problem you solved, capture symptom → root cause → fix
-  (tag it `issue`) so it's findable later — even one solved in passing is worth
-  two lines, so it isn't diagnosed from scratch next time.
+- When you fix a problem — even one solved in passing — record it as its own
+  issue (create_task(kind="issue")) with symptom → root cause → fix in the body,
+  NOT as a work-log line on whatever task happened to be open. An issue is
+  corrective work with its own lifecycle; recording it discretely (optionally
+  linked via arose_from_id to the task it came from, and system_ids to the
+  subsystem it touches) is what makes it findable so it isn't diagnosed from
+  scratch next time.
 
 Compaction hygiene — recommend compacting at clean seams. Because you record
 progress as you go, a context compaction is SAFE: the durable state lives in