✨ Add spire:project skill and update template hint

New skill loads .claude/spire/project.md at agent startup with
fallback to the bundled blank template.  Blank template now hints
the user to run /spire:init.

plugins/spire/skills/igor/references/project.md

@@ -1,3 +1,4 @@
+<!-- This is the blank template. Run /spire:init to generate a project-specific override. -->
 # Project Knowledge (per-project — swap this file when adopting Igor)
 
 Project-specific facts for Igor and the athanor. The generic behavior files

plugins/spire/skills/project/SKILL.md

@@ -0,0 +1,9 @@
+---
+name: project
+description: Loads per-project Spire configuration (override or bundled template).
+allowed-tools: Bash(cat:*)
+---
+
+!`cat "${CLAUDE_PROJECT_DIR}/.claude/spire/project.md" 2>/dev/null || cat "${CLAUDE_SKILL_DIR}/../igor/references/project.md"`
+
+<!-- If the above block is the blank template, run /spire:init to configure this project. -->