webui: Use `toLocaleString()` format consistently across chat message statistics

Start with tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessageStatistics/ChatMessageStatistics.svelte and inspect how each listed statistic is currently rendered, including values using toFixed(2). Choose a consistent locale-formatting approach based on the issue's alternatives, then verify in the web UI that all listed chat statistics display consistently.

Prerequisites

• I am running the latest code. Mention the version if possible as well.
• I carefully followed the README.md.
• I searched using keywords relevant to my issue to make sure that I am creating a new issue that is not already open (or closed).
• I reviewed the Discussions, and have a new and useful enhancement to share.

Feature Description

llama.cpp's web UI currently sometimes uses locale formatting only for certain components like Total Tokens Generated and Generated Tokens. This issue proposes to consistently use this locale formatting across chat message statistics.

Motivation

It is generally much easier to glance at values that use locale formatting than unformatted ones. This will also make llama.cpp's web UI format more consistent with the changes made in #18300 that were missed in PR's made after it.

Possible Implementation

This would just require editing tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessageStatistics/ChatMessageStatistics.svelte by adding .toLocaleString() at the end of variables that we want formatted.

We may also want to add locale formatting to stats currently printed using .toFixed(2). To format accordingly, we can either:

• Use in-line options parameter in .toLocaleString(locale, options) instead of the above (e.g. .toLocalString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 })
• Use a common number formatter (e.g. new Intl.NumberFormat(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}))

I personally think that creating a common formatter might be the best way to do this, since it is commonly used across 3 separate variables.

Once we choose one of the two above methods for the toFixed(2) replacement, I can write a PR where I update:

• tokensPerSecond
• agenticTimings!.toolCallsCount
• promptTokens
• agenticToolsPerSecond
• promptTokens
• promptTokensPerSecond