feat: user-scoped history/delete/rollback, dashboard & login UI, ignore *.pem

- Filter history/rollback/delete by user_id in secrets-core
- MCP tools/web pass user context; dashboard refresh; favicon static
- .gitignore *.pem; vscode tasks tweaks
- clippy: collapse else-if in rollback latest-history branch

Made-with: Cursor

crates/secrets-mcp/static/favicon.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
+  <text x="16" y="23" text-anchor="middle" font-family="system-ui,Segoe UI,sans-serif" font-size="22" font-weight="700" fill="#58a6ff">S</text>
+</svg>