## Motivation and Context
The MCP specification constrains `Annotations.priority` to the 0–1 range
(`@minimum 0`, `@maximum 1`), but the Ruby SDK accepts any value. The other
official SDKs already enforce this (TypeScript, Python, and PHP).
This follows the existing pattern in `MCP::Icon`, which validates its
constrained `theme` value in the constructor and raises `ArgumentError`.
## How Has This Been Tested?
Added tests in `test/mcp/annotations_test.rb`:
- valid `priority` at the lower (0) and upper (1) bounds is accepted
- out-of-range `priority` (above 1, below 0) raises `ArgumentError`
The full unit suite and RuboCop pass locally.
## Breaking Changes
Strictly speaking yes: a caller that currently passes an out-of-range
`priority` (e.g. `priority: 99`) will now get an `ArgumentError`. Such values
already violate the MCP specification, and `nil` / in-range values are
unaffected.
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