feat(mcp): proactive project bootstrapping at session start

Adds an always-on _INSTRUCTIONS directive: when work touches Scribe and
no project is in scope, search for a related project and propose
enter_project (confirm first), or offer to create one (confirm name/goal
first) — never silently adopt or create. Pairs with the enter_project
handshake and the host-memory pointer directive. Closes scribe task #585.

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

src/fabledassistant/mcp/server.py

@@ -89,6 +89,17 @@ summary, open tasks, and recent notes — everything you need to know the lay of
 the land before mutating. Don't call get_project + get_applicable_rules + a
 search separately when enter_project already composes them.
 
+Don't wait to be told which project you're in. At the start of a session that
+touches Scribe — or the moment work clearly belongs to a project but none is in
+scope — bootstrap project context proactively: search for a related existing
+project (search / list_projects, matching on the work's subject, the repo or
+directory name, and recent activity). If you find a confident match, propose it
+and call enter_project once the operator confirms. If nothing matches, offer to
+create a project, confirming its name and goal first. Always confirm before
+adopting or creating — never do either silently, and never guess a project into
+existence. Once a project is in scope, the enter_project handshake and the
+host-memory pointer step above both apply.
+
 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