chore: fix preview routes, MarkdownRenderer, update opencode config

- _preview_routes.py: fix preview endpoint params for multi-language
- MarkdownRenderer.svelte: renderer fixes for assistant messages
- speckit.analyze.md: update opencode command for spec analysis
- opencode.jsonc: config alignment

.opencode/opencode.jsonc

@@ -13,7 +13,7 @@
         "axiom": {
       "type": "local",
       "command": ["sh", "-c","/home/busya/dev/axiom-mcp-rust-port/target/release/axiom-mcp-server-rs 2>>/tmp/axiom-server.log"],
-      "enabled": true
+      "enabled": false
     }
   }
 }