chore(mcp): tighten plan-instruction to override .md plan habit

The prior wording ("not in local .md files") was a footer after a
how-to and lost to the much louder superpowers brainstorming /
writing-plans skill flow, which terminates by saving to
docs/superpowers/specs/*.md and docs/superpowers/plans/*.md.

Reorder so start_planning is named as the FIRST action, explicitly
override the .md skill paths, and extend the rule to cover specs as
well as plans (matches the rulebook's rule 27).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/fabledassistant/mcp/server.py

@@ -48,11 +48,15 @@ rules via create_rule when you notice a pattern worth codifying — coordinate
 with the operator on whether it belongs in an existing rulebook+topic or a
 new one.
 
-Plans are tasks with kind=plan. Begin a plan with start_planning(project_id,
-title) — that seeds a plan template and returns the project's applicable_rules.
-Maintain the plan with the normal task tools (update_task for the body,
-add_task_log for progress); its work-logs are the build record. Build plans in
-Scribe via start_planning, not in local .md files.
+Plans are tasks with kind=plan, and Scribe is the canonical home for them.
+When you begin non-trivial work, call start_planning(project_id, title) FIRST —
+before any brainstorming, design, or plan-writing skill runs. start_planning
+seeds the plan body, returns the project's applicable_rules, and gives you the
+task id you'll write into. If a skill or habit tells you to save a plan or spec
+to `docs/superpowers/plans/*.md` or `docs/superpowers/specs/*.md`, that path is
+superseded here: put the spec/plan content in the kind=plan task's body via
+update_task, and record progress with add_task_log. Local .md files are not
+the record — the task is.
 
 Deletes are recoverable: every delete_* tool moves the entity (and its
 descendants) to the trash and returns a deleted_batch_id. Use list_trash() to