fix: implement getJsonSchema and harden OAuth/tool payloads

[superdav42]

Summary

• Resolves fatal error where `AnthropicOAuthRequestAuthentication` was abstract due to the missing `getJsonSchema()` method required by `WithJsonSchemaInterface`. Now extends `ApiKeyRequestAuthentication` and provides an empty schema (tokens come from the pool, not user input).
• Always prepends the Claude Code system identifier — the OAuth gateway returns a misleading 401 without it.
• Normalizes tool `input_schema` so empty `properties` serialize as `{}` (not `[]`) and list-style `items` are coerced to `{}`, satisfying Anthropic's draft-2020-12 validator.
• Strips `#state` fragment from authorization codes before token exchange.
• Logs token-refresh failures to `debug.log`.
• Drops `strict_types` from `plugin.php` bootstrap (incompatible with the WP plugin loader).

Test plan

• Plugin activates without fatal
• OAuth login completes end-to-end
• Chat with tools works through the Anthropic Max provider