Pitch

opencode parity. We have `crates/tui/src/lsp/` foundation (#136) but it isn't surfaced in the transcript yet. After every `apply_patch` / `edit_file` / `write_file`, send a `textDocument/didChange` to the LSP server and wait briefly (~300ms) for diagnostics. Render any errors / warnings inline below the patch result:

```
✓ apply_patch crates/tui/src/foo.rs

• 5 lines
  ⚠ rust-analyzer · 1 error · 1 warning
  foo.rs:12:9 expected ;, found }
  foo.rs:18:5 unused variable: x
  ```

The model sees these in the next turn (already in the tool result text), so it can self-correct without the user having to paste the build error.

Implementation sketch

• LSP server discovery already exists; just poll `pull_diagnostics` after each patching tool call.
• Cap diagnostic rendering at 5 most-severe entries per file.
• Setting to disable for users on slow LSP servers (`/config diagnostics_inline false`).

Acceptance

• Patching a Rust file with a syntax error shows the error inline in the tool result.
• Diagnostics auto-clear when the next patch fixes them.
• No regression for languages without an LSP installed.
• Setting toggle works.