chore: update smithery dockerfile to be closer to the official one

[nirinchev]

Proposed changes

Checklist

• I have signed the MongoDB CLA

[Copilot]

Pull Request Overview

This PR updates the Smithery Dockerfile to align with the official Docker image structure and security practices.

• Updates user creation commands to use addgroup/adduser pattern instead of single adduser command
• Changes working directory from /app to /home/mcp for better security practices
• Updates the COPY command in the production stage to reference the new working directory path

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[Copilot]

When using a non-root user, ensure the working directory is owned by that user. Add RUN chown -R mcp:mcp /home/mcp after creating the user to ensure proper permissions.

[coveralls]

Pull Request Test Coverage Report for Build 17657973871

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 185 unchanged lines in 17 files lost coverage.
• Overall coverage increased (+0.4%) to 81.59%

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Files with Coverage Reduction	New Missed Lines	%
src/tools/atlas/create/createAccessList.ts	1	90.91%
src/tools/atlas/read/inspectAccessList.ts	3	86.67%
src/tools/atlas/create/createDBUser.ts	4	93.55%
src/tools/atlas/read/listAlerts.ts	5	66.67%
src/telemetry/eventCache.ts	6	82.61%
src/resources/common/exportedData.ts	7	68.47%
src/tools/atlas/read/listDBUsers.ts	8	80.3%
src/tools/atlas/read/listProjects.ts	11	67.19%
src/common/logger.ts	12	92.97%
src/tools/atlas/atlasTool.ts	12	26.67%

Totals
Change from base Build 17476889967:	0.4%
Covered Lines:	4866
Relevant Lines:	5864

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💛 - Coveralls