fix: path validation bypass, agent collision, and skill impact inflation (#112)

- Replace str.startswith() path checks with Path.relative_to() in
  uninstall, update, and backup commands (matching install.py pattern)
- Prevent extension agents from silently overwriting core agents with
  same name in AgentRegistry._discover_tiered_agents()
- Distribute quality_impact across applied skills instead of attributing
  full delta to each skill individually
- Fix temp file leak in backup when tar.add() throws
- Fix type annotation dict[str, any] -> dict[str, Any] in ComponentRegistry
- Regenerate ARCHITECTURE.md with full GitNexus knowledge graph analysis

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: Tony363

AGENTS.md

@@ -106,7 +106,7 @@
 <!-- gitnexus:start -->
 # GitNexus — Code Intelligence
 
-This project is indexed by GitNexus as **SuperClaude** (8999 symbols, 21160 relationships, 300 execution flows). Use the GitNexus MCP tools to understand code, assess impact, and navigate safely.
+This project is indexed by GitNexus as **SuperClaude** (8994 symbols, 21155 relationships, 300 execution flows). Use the GitNexus MCP tools to understand code, assess impact, and navigate safely.
 
 > If any GitNexus tool warns the index is stale, run `npx gitnexus analyze` in terminal first.