🪲 BUG: Fix messages blending together across tool calls

[FernandoCelmer]

pycodeloop's serve.py has emitted a chat/turnEnd notification after every provider turn since dotflow-io/pycodeloop@fa0689f — but this extension never listened for it. FORWARDED_NOTIFICATIONS (chat.types.ts) didn't include it, so the webview never got a signal to close the current assistant bubble at a tool-call boundary.

Symptom: narration text before a tool call (e.g. "Sure, let me check that file:") and the model's final answer after the tool result get concatenated into the same bubble instead of appearing as separate turns — the tool-call card renders as a separate element sandwiched between them, but the text silently merges. Over a multi-tool-call run this reads as the assistant "losing track" of what it's saying.

Root cause: appendAssistantDelta reuses the existing assistantTurn object if one is still open. Nothing ever closed it between turns — only case "done" did, once, at the very end of the whole run.

Fix: forward chat/turnEnd, handle it by closing the current bubble (finishAssistantTurn()) so the next textDelta starts a fresh one. Added a turnEndSeen flag so case "done"'s fallback-text render (needed for CLI versions older than turnEnd's introduction) doesn't duplicate the last bubble when turnEnd already closed it.

Test plan

• npm test (43 passed) / npx tsc --noEmit / npm run lint clean
• Traced through single-turn, multi-tool-call, and no-turnEnd (old CLI) scenarios by hand — see PR description above