build(deps): bump rust from 1.93-slim-trixie to 1.95-slim-trixie in /app-server

[dependabot]

Bumps rust from 1.93-slim-trixie to 1.95-slim-trixie.

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Note

Low Risk
Low risk: this only updates the Rust toolchain used in the build container, with no code or runtime image changes beyond potential compile-time differences.

Overview
Updates app-server/Dockerfile to build with Rust 1.95-slim-trixie instead of 1.93-slim-trixie, keeping the rest of the multi-stage build unchanged.

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