v0.7.6 — surface mid-stream errors

Web — v0.7.6

• Mid-stream errors no longer vanish. When an upstream model server failed after it had already started streaming (e.g. a provider erroring out as it goes to emit a tool call), the turn died silently — you'd see the reasoning block, then nothing, then the copy/retry buttons, as if the model had simply stopped. The error is now surfaced in the UI with a retry, regardless of how far the response had streamed. Closes #40.
• No more stranded half-answers. A turn that errored mid-stream was being persisted as a partial, reasoning-only message, so the dangling "Thought for Ns" block survived a page reload with no answer and no way to recover. Failed turns are now dropped instead of saved.

Docker image: ghcr.io/yoloyash/overtchat-app:0.7.6 — same docker compose pull && docker compose up -d upgrade path.

Full Changelog: v0.7.5...v0.7.6