fix(web): stop clipping diff filename descenders

[rynfar]

Diff file names with descenders are clipped by Pierre's start-ellipsis container when the inherited line-height is one em. Give only the clipped current and previous names a 16px line box, preserving the 32px header metric and metadata alignment. Remove the clipped hover underline while retaining the hover color, Pylon appearance, worker lifecycle and reduced-motion behavior.

Ports T3 source c18e5ea6ed741443a8ec4a5d22d4b6939b0ecd21 (#14375), one source path, under the bounded arrivals cycle (parent audit #865). Web and Electron share this component; native mobile has a separate renderer.

Verification: all 3 existing StyledDiffCodeView worker/option tests pass; scoped lint/format and diff checks pass. Source review confirms 16px names plus 12px padding remain within diffHeaderHeight: 32. No new tests for this reversible CSS adjustment. Rendered before/after evidence is below. No rendered clipping/zoom/custom-theme claim; no motion change or native/device action.

Model: GPT-6 / Codex desktop harness.

Rendered evidence

Isolated dev servers (base origin/pylon vs. this change merged with the other web drafts), real Claude turn editing glyph-sampling.ts / typography-jgpqy.md, Diff panel → Latest turn.

Before	After

Measured in the shadow DOM [data-title]: before line-height: 12px, scrollHeight 13 > clientHeight 12 with overflow: hidden and underline (descenders of g/p/y clipped); after line-height: 16px, scrollHeight 16 == clientHeight 16, no underline.

Independent adversarial review: no findings (byte-identical to upstream c18e5ea6).

Evidence and review by Claude Opus 5.5 in Claude Code.

[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	14.0 KiB	14.0 KiB	+1 B (+0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.3 KiB	7.3 KiB	−13 B (−0.2%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.7 KiB	6.7 KiB	+14 B (+0.2%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.0 KiB	58.0 KiB	+44 B (+0.1%)	66.4 KiB	✅
Codex	Live turn messages	9	10	+1 (+11.1%)	21	✅
Claude	Total thread wire	14.0 KiB	14.0 KiB	+9 B (+0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.3 KiB	7.3 KiB	−24 B (−0.3%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.8 KiB	+33 B (+0.5%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.9 KiB	58.9 KiB	+44 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	9	10	+1 (+11.1%)	21	✅

Baseline: b5a607e · PR result: 5707dc2 · 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: 115.7 KiB
• Claude decoded thread snapshot: 116.4 KiB

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