feat(KB-328): bundle Fusion skill with CLI package for agent interoperability

- Add bundled Fusion skill at packages/cli/skill/fusion/ with SKILL.md and reference docs
- Include workflow guides for task lifecycle, specifications, dashboard CLI, and task management
- Add reference docs for CLI commands, extension tools, capabilities, best practices, and patterns
- Add postinstall script to sync skill into ~/.pi/agent/skills/fusion on install
- Add skill-sync test coverage and changeset for minor version bump

packages/cli/skill/fusion/references/skill-patterns.md

@@ -0,0 +1,38 @@
+# Skill Patterns Analysis
+
+## Patterns Observed from High-Quality Skills
+
+### 1. Router Pattern (create-skill)
+
+- SKILL.md acts as a router with `<routing>` section
+- Maps user intent to specific workflow files
+- Essential principles are inline in SKILL.md (always loaded)
+- Workflows have `<required_reading>`, `<process>`, `<success_criteria>`
+- References contain reusable domain knowledge
+
+### 2. Command Reference Pattern (agent-browser)
+
+- Core workflow presented upfront (navigate → snapshot → interact → re-snapshot)
+- Essential commands with examples inline
+- Common patterns section for frequent use cases
+- Deep-dive references linked at the bottom via table
+- Templates for ready-to-use scripts
+- Uses `allowed-tools` for Bash commands
+
+### 3. Search & Discover Pattern (find-skills)
+
+- Simple single-file skill (no router needed)
+- Clear "When to Use" triggers section
+- Step-by-step guidance for common flow
+- Fallback guidance when primary path fails
+- Tips section for optimization
+
+## Key Takeaways for Fusion Skill
+
+1. **Use router pattern** — Fusion has multiple distinct workflows (task management, lifecycle, specs, dashboard/CLI)
+2. **No `allowed-tools` needed** — Fusion tools are registered via pi extension, not Bash CLI
+3. **Inline essential concepts** — Task columns, workflow overview in SKILL.md
+4. **Progressive disclosure** — SKILL.md routes to workflows, workflows reference detailed docs
+5. **Pure XML structure** — No markdown headings (#, ##, ###) in body
+6. **Triggers section** — Clear when-to-use criteria
+7. **Under 500 lines** — Keep SKILL.md concise, split to workflows/references