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>

plugin/skills/systematic-debugging/SKILL.md

@@ -10,8 +10,9 @@ guessed fix that "seems to work" often just moves the bug somewhere else.
 
 ## Recall first
 
-Before digging in, `search` Scribe for the symptom — a prior `issue` note may
-already hold the cause and the fix. Don't re-debug what's already solved.
+Before digging in, `search` Scribe for the symptom — a prior issue
+(`list_tasks(kind="issue")` or `search`) may already hold the cause and the fix.
+Don't re-debug what's already solved.
 
 ## The loop
 
@@ -29,7 +30,10 @@ already hold the cause and the fix. Don't re-debug what's already solved.
 
 ## Capture the issue (so it's findable)
 
-When resolved, record it in Scribe (`create_note`, tag `issue`): **symptom →
-root cause → fix → how it was verified**. Even a problem fixed in passing is
-worth two lines — that's how the next person (or you) avoids re-deriving it. If
-the fix was tracked as a task, log the resolution there and set it `done`.
+When resolved, record it in Scribe as its own issue (`create_task(kind="issue")`):
+**symptom → root cause → fix → how it was verified** in the body, optionally
+linked to the task it arose from (`arose_from_id`) and the subsystem it touches
+(`system_ids`). Even a problem fixed in passing is worth two lines — that's how
+the next person (or you) avoids re-deriving it. Record it discretely; don't bury
+it as a work-log line on an unrelated open task. If the work was already tracked
+as its own task, log the resolution there and set it `done`.