feat(skill): add team-arch-opt architecture optimization skill

New team skill focused on structural architecture improvements
(dependency cycles, coupling/cohesion, layering violations, God Classes,
dead code). Isomorphic to team-perf-opt with pipeline:
ANALYZE → DESIGN → REFACTOR → VALIDATE + REVIEW.

Roles: coordinator, analyzer, designer, refactorer, validator, reviewer.
Supports single/fan-out/independent/auto parallel modes.

.claude/skills/team-arch-opt/subagents/explore-subagent.md

@@ -0,0 +1,113 @@
+# Explore Subagent
+
+Shared codebase exploration for discovering architecture-critical structures, dependency graphs, module boundaries, and layer organization. Results are cached to avoid redundant exploration across analyzer and refactorer roles.
+
+## Design Rationale
+
+Codebase exploration is a read-only operation shared between analyzer (mapping structural issues) and refactorer (understanding implementation context). Caching explorations avoids redundant work when refactorer re-explores structures the analyzer already mapped.
+
+## Invocation
+
+Called by analyzer, refactorer after needing codebase context for architecture analysis or implementation:
+
+```
+Task({
+  subagent_type: "cli-explore-agent",
+  run_in_background: false,
+  description: "Explore codebase for architecture-critical structures in <target-scope>",
+  prompt: `Explore the codebase to identify architecture-critical structures.
+
+Target scope: <target-scope>
+Session: <session-folder>
+Focus: <exploration-focus>
+
+Tasks:
+1. Map the module structure, entry points, and layer boundaries within scope
+2. Build dependency graph (import/require relationships between modules)
+3. Identify architectural patterns (layering, dependency injection, event-driven, plugin architecture)
+4. Note any existing abstractions, interfaces, and module boundaries
+5. List key files with their roles, layer assignment, and dependency relationships
+
+Output a structured exploration report with:
+- Module map (key files, their relationships, and layer assignments)
+- Dependency graph (directed edges between modules, cycle indicators)
+- Layer structure (identified layers and their boundaries)
+- Existing architectural patterns found
+- Architecture-relevant configuration (path aliases, barrel exports, module boundaries)`
+})
+```
+
+## Cache Mechanism
+
+### Cache Index Schema
+
+`<session-folder>/explorations/cache-index.json`:
+
+```json
+{
+  "entries": [
+    {
+      "key": "<scope-hash>",
+      "scope": "<target-scope>",
+      "focus": "<exploration-focus>",
+      "timestamp": "<ISO-8601>",
+      "result_file": "<hash>.md"
+    }
+  ]
+}
+```
+
+### Cache Lookup Rules
+
+| Condition | Action |
+|-----------|--------|
+| Exact scope+focus match exists | Return cached result from <hash>.md |
+| No match | Execute subagent, cache result to <hash>.md, update index |
+| Cache file missing but index has entry | Remove stale entry, re-execute |
+| Cache older than current session | Use cached (explorations are stable within session) |
+
+## Integration with Calling Role
+
+The calling role is responsible for:
+
+1. **Before calling**: Determine target scope and exploration focus
+2. **Calling**: Check cache first, invoke subagent only on cache miss
+3. **After calling**:
+
+| Result | Action |
+|--------|--------|
+| Exploration successful | Use findings to inform analysis/implementation |
+| Exploration partial | Use available findings, note gaps |
+| Exploration failed | Proceed without exploration context, use direct file reading |
+
+## Output Schema
+
+```json
+{
+  "scope": "<target-scope>",
+  "module_map": [
+    { "file": "<path>", "role": "<description>", "layer": "<presentation|domain|data|infra>", "dependency_graph": { "imports": ["<path>"], "imported_by": ["<path>"] } }
+  ],
+  "dependency_graph": {
+    "nodes": ["<module-path>"],
+    "edges": [{ "from": "<path>", "to": "<path>", "type": "<import|re-export|dynamic>" }],
+    "cycles": [["<path-a>", "<path-b>", "<path-a>"]]
+  },
+  "layer_structure": [
+    { "layer": "<name>", "modules": ["<path>"], "violations": ["<description>"] }
+  ],
+  "existing_patterns": [
+    { "type": "<pattern>", "location": "<file:line>", "description": "<what>" }
+  ],
+  "investigation_targets": ["<file-or-pattern>"]
+}
+```
+
+## Error Handling
+
+| Scenario | Resolution |
+|----------|------------|
+| Single exploration angle fails | Continue with partial results |
+| All exploration fails | Return basic result from direct file listing |
+| Target scope not found | Return error immediately |
+| Cache corrupt | Clear cache-index.json, re-execute |