fix(explorer): polish responsive contract source viewer

[snario]

The contract source viewer crowded the code with a fixed-width sidebar and a gray canvas. Use a white light-mode canvas, enable line wrapping by default, and collapse the sidebar when the viewer is narrower than 1,000px. Users can toggle the sidebar and wrapping; selecting a file closes navigation on compact layouts.

Tighten the toolbar, adapt the panel height to the viewport, and retain the current outlined file selection.

Validation: root pnpm check (including type checks), pnpm check:types, explorer tests (205 passed), and pnpm precommit. Browser-checked responsive layout, file navigation, wrapping, and dark mode; verified the real PathUSD page against live testnet data.

Screenshots

Before is the reported layout; after is the real local explorer with the updated viewer.

Before	After

[github-actions]

Bundle Size Report

Metric	Size	Δ Change
Total	17.3 MB	+13.1 MB (+309.4%)
Gzip	3.9 MB	+2.7 MB (+219.2%)
Brotli	3.3 MB	+2.2 MB (+209.0%)

Chunk changes (>1KB)

Chunk	Change
assets/chains.js (removed)	-360.7 KB
assets/tempo-queries.js	-301.0 KB
assets/core.js (removed)	-189.5 KB
assets/export-rate-limit.js (removed)	-177.3 KB
assets/engine-javascript.js (removed)	-92.9 KB
assets/decodeAbiParameters.js (removed)	-71.7 KB
assets/_hash.js	-36.1 KB
assets/react.js	-31.8 KB
assets/AbiItem.js (removed)	-27.1 KB
assets/sha2.js (removed)	-14.7 KB
assets/queryOptions.js	-11.8 KB
assets/Bytes.js	-9.6 KB
assets/Amount.js	-9.6 KB
assets/env.js	-9.2 KB
assets/DataGrid.js	-6.7 KB
assets/fee-amm-pool-rows.js (removed)	-6.6 KB
assets/validators.js (removed)	-5.1 KB
assets/token.js	-5.1 KB
assets/tokens.js	-1.1 KB
assets/Value.js (removed)	-1.0 KB
...and 356 more

Compared against main branch (baseline from 4/27/2026, 4:02:54 PM)