fix(verifier): validate configuration precedence

[kvinwang]

Problem

Verifier assembled settings from defaults, file/environment, and CLI in an order that could let a lower-priority source overwrite an explicit higher-priority value. The service then ran with different trust/network settings than the operator requested.

Root cause and fix

Apply and validate configuration sources in the documented precedence order, preserving explicit overrides.

Implementation

The branch records the following focused implementation work:

• fix(verifier): validate configuration precedence
• fix(verifier): escape image template diagnostic

Changed paths:

• dstack/dstack-attest/src/attestation.rs
• dstack/dstack-types/src/lib.rs
• dstack/verifier/src/main.rs

Scope

This PR addresses one logical verifier finding. It intentionally excludes the acceptance-test infrastructure from #841 and unrelated product fixes from #840.

Dependency and merge order

This PR is based directly on master and does not require another split product PR to merge first.

Verification

• git diff --check origin/master..origin/codex/fix-verifier-config-precedence: passed.
• The declared base was verified as an ancestor of the PR head.
• Focused compile/check verification was run for the changed component where applicable; non-Rust packaging or configuration changes were reviewed against their exact branch delta.

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