Fix destructiveHint/openWorldHint coerced to true when explicitly false

[rickreyhsig-wealthbox]

Summary

Fixes #143.

Annotation#initialize reads destructiveHint/openWorldHint with annotation["key"] || default. Since both default to true, an explicit false from the server (false || true) is silently discarded and replaced with true. readOnlyHint/idempotentHint don't have this problem — their defaults are already false, so || never overrides an explicit value either way.

RubyLLM::MCP::Annotation.new({"destructiveHint" => false}).destructive_hint
# => true (should be false)

Fix

Swapped || for fetch(key, default), which only applies the default when the key is absent from the hash — an explicit false (or true) passes through untouched:

@destructive_hint = annotation.fetch("destructiveHint", true)
@open_world_hint  = annotation.fetch("openWorldHint", true)

Tests

Updated the existing RubyLLM::MCP::Annotation spec block in tool_spec.rb, which had a test explicitly documenting the old (buggy) behavior — flipped it to assert the correct behavior instead, and dropped stale comments elsewhere in that block referencing the old || semantics.

Verified directly against the real RubyLLM::MCP::Annotation class (Ruby 3.2, gem's own dependency chain) for both the fixed fields and the two fields that were already correct — all pass:

PASS: explicit false destructiveHint preserved (got false, expected false)
PASS: explicit false openWorldHint preserved (got false, expected false)
PASS: missing destructiveHint defaults true (got true, expected true)
PASS: missing openWorldHint defaults true (got true, expected true)
PASS: explicit true destructiveHint stays true (got true, expected true)
PASS: explicit true openWorldHint stays true (got true, expected true)
PASS: readOnlyHint unaffected (got false, expected false)
PASS: idempotentHint unaffected (got false, expected false)

I wasn't able to run the full spec suite locally — tool_spec.rb's before(:all) spins up the fixture MCP servers over bun, and getting those running requires installing @modelcontextprotocol/sdk for each fixture app individually, which felt out of scope for verifying this change. Happy to do so if that's actually needed for review.