fix(hetzner): reject malformed API prices

[aiirvizionz]

Summary

• reject malformed Hetzner API price strings instead of partially parsing them
• use the same strict decimal parsing for quotes, server selection, and volume rates
• add focused coverage for valid, malformed, and non-decimal values

Validation

• .\\node_modules\\.bin\\vitest.cmd run packages/cloud/hetzner/src/index.test.ts packages/cloud/hetzner/src/price.test.ts
• .\\node_modules\\.bin\\tsc.cmd -p packages/cloud/hetzner/tsconfig.json --noEmit
• git diff --check

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🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.