[STACKED on #941] fix(kms): bound the authorization boot schema

[kvinwang]

STACKED PR — merge #941 first.

Problem

The authorization boot payload/schema accepted unbounded or structurally unconstrained data. A malformed backend response could consume excessive resources or introduce unsupported fields/state during KMS startup.

Root cause and fix

Define and enforce the supported boot schema, including size/count bounds, before installing authorization state.

Implementation

The branch records the following focused implementation work:

• fix(kms): bound authorization boot schema
• fix(kms): preserve unprefixed auth measurements

Changed paths:

• dstack/kms/auth-eth-bun/index.test.ts
• dstack/kms/auth-eth-bun/index.ts

Scope

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

Dependency and merge order

• Parent PR: fix(kms): synchronize authorization Bun locks #941
• GitHub base branch: codex/fix-kms-auth-locks
• Merge the parent first; this PR contains only the additional delta above that parent.

Verification

• git diff --check origin/codex/fix-kms-auth-locks..origin/codex/fix-kms-auth-boot-schema: 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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