feat(web): compact the Discussion exchange panes

Reasoning collapses to a two-sentence plain-text preview with a Show
reasoning toggle; the full stream opens into a bounded scroller instead of
a fixed-height box that left most of the pane empty. Tool calls become one
summary line with per-tool counts. The Fusion pane decodes the streaming
result envelope so the reader sees the answer text, not raw JSON.

Author: elkaix

.changeset/discussion-compact-exchange.md

@@ -0,0 +1,5 @@
+---
+"@pymodel/pythinker-code": patch
+---
+
+Compact the Discussion exchange: reasoning shows its first two sentences with a Show reasoning toggle, tool calls collapse to one summary line, and the Fusion answer streams as text instead of its raw JSON envelope.

apps/pythinker-code/dist-web/.web-bundle-manifest.json

@@ -1,4 +1,4 @@
 {
-  "sourceHash": "7a1b7704c14c4beec0d6d07bb4512ba5d4330b477ea2da706a0f19b12bf97809",
-  "sourceFileCount": 418
+  "sourceHash": "cb40c0019f73306c93c92f7df987974702db285667c1228a3e878d839c12253b",
+  "sourceFileCount": 421
 }