feat(web): color handoff model names with their provider brand color

[maria-rcks]

Context handoff model names inherited the divider's muted color. Match each model label to its provider logo color in light and dark themes and use medium weight, preserving the divider's failed-handoff tone.

Verified on Blacksmith: web typecheck, web lint, and all 66 MessagesTimeline tests passed. Before/after captures use the same real handoff in both themes. Failed-handoff appearance was not exercised because the snapshot contains only ready handoffs.

Codex → Claude handoff, where the color difference is visible (Claude's #d97757; OpenAI, Grok, Pi, Cursor and OpenCode logos are near-black / near-white, so their names match the foreground):

Written by gpt-6-astra (Codex) in T3 Code; claude evidence and rebase by claude-fable-5-1 (Claude Code) in T3 Code

[macroscopeapp]

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — This is a small, self-contained presentation change that only colors existing handoff labels and does not alter handoff execution, schemas, or infrastructure. A Medium-severity finding remains about failed handoffs losing their destructive text tone when provider colors are applied.

Not approved because:

• 1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

No code changes detected at ec85294. Prior analysis still applies.

^{Adjust the Minimum Blocking Severity for this repo — including turning it Off — in Settings. You can add or adjust custom eligibility rules. Learn more.}