[FEATURE]: Total diffs counter in sidebar

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

A total diffs counter in the sidebar¹, showing the total number of lines of code added and deleted in a session. Currently, only individual diff counters for each modified file are shown.

This is helpful for assessing the total work of an agent and fits naturally into the interface.

Footnotes

1. https://github.com/anomalyco/opencode/blob/dev/packages/opencode/src/cli/cmd/tui/routes/session/sidebar.tsx ↩

[ariane-emory]

@aarvinr I tried taking a stab at this myself and what the clankers came up with was virtually identical: ariane-emory#200.

The only difference appears to be the choice between two separate reduce calls or a single reduce call with an object argument as the accumulator. The bot assures me that a single reduce is likely slightly more efficient, but I'm sure that the difference is probably trivial and not worth worrying about.

In other words, LGTM.