feat(web): unify touch resize interactions

[btli]

Related issue

N/A — consolidates draft PRs #4780, #4781, #4782, #4784, #4785, and #4786.

Summary

This draft replaces the six touch-interaction drafts with one current-main implementation. It unifies pointer capture, cancellation, persistence, accessible separators, and carefully bounded hit gutters across the sidebar, inline workspace rail, terminal-list column, push panels, and comments panel. It also centralizes viewport and input-capability detection for web and Android.

ELI5: the thin dividers between app panes now have a larger invisible grab area, so a finger or stylus can resize them without covering nearby buttons or scrollbars.

sidebar | chat | inline rail | push panel
                 terminal list | terminal
file viewer | comments
       touch / pen / mouse / keyboard

Supersedes (but does not close): #4780, #4781, #4782, #4784, #4785, #4786.

Test Plan

• bun --bun run test -- <17 touched Vitest files> — 623 passed, 1 expected failure.
• uv run --group test pytest -q <5 touched e2e_ui files> — 5 passed.
• Android OmnigentWebViewClientTest — 20 passed.
• bun --bun run lint, bun --bun run type-check, and bun --bun run build — passed.
• uv run pre-commit run --all-files — all applicable hooks passed; the current upstream uv.lock normalizer baseline was excluded because it rewrites an unrelated lockfile.
• Mutation checks: every production-backed touched test file failed against the origin/main production tree, then passed with this implementation restored.

Demo

Android foldable/tablet touch-interactions video (Show taps enabled; touch dot visible)

The single recording covers folding/form-factor changes plus sidebar, inline rail, terminal-list column, push-panel, comments-panel, and adjacent-scroll seam behavior.

Type of change

• Bug fix
• Feature
• UI / frontend change
• Refactor / chore
• Docs
• Test / CI
• Breaking change

Test coverage

• Unit tests added / updated
• Integration tests added / updated
• E2E tests added / updated
• Manual verification completed
• Existing tests cover this change
• Not applicable

Coverage notes

Manually verified the Android foldable/tablet recording with Developer Options “Show taps” enabled, including the visible touch dot and each resize/scroll seam represented by the six superseded drafts.

Changelog

Pane dividers are now easier and more reliable to resize with touch, stylus, mouse, or keyboard.