docs: Update Live Browser preview documentation to match implementation

[numnx]

This updates the sprint browser preview documentation across docs/ and docs-web/ to be aligned with the actual implementation and tooling APIs available in Code UX.

Changes:

• Corrects docs/architecture/sprint-preview-browser.md API surface table to include both browser/sessions and projects/:projectId/sprints/:sprintId/preview/sessions/ endpoints.
• Highlights that preview sessions are explicitly scoped per project/sprint pair.
• Updates docs/dashboard/browser-preview.md to specify that rebuild, stop, and remove track distinct pending actions.
• Clarifies port mapping support, stating that multiple container ports map to explicit loopback addresses and render as distinct tabs.
• Corrects script workflow in docs-web/user/dashboard/browser-preview.md and replaces get_script with update_script where it implies saving behaviors.
• Updates docs-web/user/troubleshooting.md to point users to the dashboard logs/MCP tools instead of using docker ps.
• Syncs the MCP tooling capabilities in docs/mcp/tools-and-contracts.md to clarify the full set of preview actions.

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PR created automatically by Jules for task 8704166769834444643 started by @numnx

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