feat: resize human-controlled environment browser

[laotoutou]

Summary

• prefer TigerVNC for human Browser control so the remote X desktop follows the available panel size
• keep the Xvfb/x11vnc path for older coding-agent images and viewport scaling as its client fallback
• start the shared headed Chrome maximized under its normal Linux sandbox, without Playwright, CDP, automation, or --no-sandbox flags
• document the v0.4 runtime requirement and performance boundary

Depends on the already merged Sandbox0 runtime/image work in sandbox0-ai/sandbox0#800, sandbox0-ai/sandbox0#801, and sandbox0-ai/sandbox0-infra#164.

Validation

• npm test (756 passed)
• npm run typecheck
• npm run lint
• npm run openapi:check
• npm run build
• remote x86 CLI go test ./...
• remote gVisor active sandbox: RFB resize 1440x900 -> 1180x760 -> 1600x900
• remote gVisor active sandbox: Playwright guard exits 75 while the human lock exists
• RFB-only Google sign-in gate reaches Couldn't find this account after Next, without Playwright/CDP
• active headed browser cgroup usage approximately 1.09 GiB under the 2 GiB limit
• production coding-agent claim returns v0.4 with /usr/bin/Xtigervnc (1.13.1+dfsg-2build2) and is cleaned up