feat(web): use comfortable Scient typography defaults

[yaacovcorcos]

The inherited defaults and a few fixed-pixel file surfaces make Scient unnecessarily difficult to read. This gives Scient a coherent comfortable-reading baseline while preserving the existing T3 appearance controls and user overrides.

The change raises the default interface, prompt, code, and terminal sizes to 18/16/15/14 px. Four Scient-owned CSS tokens cover the important exceptions that do not inherit those settings: workspace file names, inline chat file links, compact metadata/tooltips, and diff/file headers. Rendered chat Markdown and Markdown file previews continue to share the existing renderer, so they scale without a parallel typography system.

The upstream seam remains narrow. A read-only merge simulation against the freshly fetched T3 main found exactly the same two pre-existing auth-redirect conflicts as owned main; this branch adds no new conflict. It also merges cleanly with draft PR #30.

Verification:

• 59 focused tests passed
• targeted format and lint passed
• contracts, web, and desktop typecheck passed
• web production build passed
• git diff --check passed

Manual visual acceptance is intentionally pending while this PR remains draft.

Generated with GPT-5.6 in Codex.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	11.3 KiB	11.3 KiB	+11 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	5.5 KiB	5.5 KiB	−5 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	5.9 KiB	5.9 KiB	+16 B (+0.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	49.7 KiB	49.7 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	16	16	0 (0.0%)	21	✅
Claude	Total thread wire	11.3 KiB	11.4 KiB	+16 B (+0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	5.5 KiB	5.5 KiB	−3 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	5.8 KiB	5.9 KiB	+19 B (+0.3%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	50.6 KiB	50.6 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	16	16	0 (0.0%)	21	✅

Baseline: 70b9a67 · PR result: 85ce820 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 94.6 KiB
• Claude decoded thread snapshot: 95.4 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.