[FEATURE]: Desktop: end-of-turn edited-files summary in chat (like Codex)

Problem

When an agent finishes a task in OpenCode Desktop, the chat transcript gives no compact summary of which files were actually created or edited during that turn. To find out what changed, I have to switch to the separate Git Changes / Files Changed panel or read through tool-call entries.

Codex shows the edited files at the end of each task directly in the conversation, which makes reviewing results and deciding what to open next much faster.

Proposal

After each completed agent turn, append a compact edited-files block to the chat, for example:

• Created: / Edited: / Deleted: lists of workspace-relative paths
• Optional +/- line stats per file if already available
• Each entry actionable: click to open in the built-in editor/file panel, modifier-click to reveal in the OS file manager

This pairs naturally with #37891 (file paths in chat are currently not clickable at all) — the summary block would be most useful if its entries are clickable under whatever mechanism that issue introduces.

Relation to existing features

• The existing Desktop Git Changes panel is session/workspace-scoped and a separate surface; it does not tell me what the agent changed in the turn that just finished, and it mixes in changes from other sources.
• #36151 proposes broader on-demand /recap session summaries (prose, commands, decisions, TODOs). An automatic end-of-turn edited-files list is a narrower, always-on sibling of that idea; both can coexist.

Environment

• App: OpenCode Desktop 1.18.21
• OS: Microsoft Windows 11 Education, 25H2, build 26200.8875