feat(server): adapt gpt5 (#13478)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- New Features
- Added GPT-5 family and made GPT-5/-mini the new defaults for Copilot
scenarios and prompts.

- Bug Fixes
- Improved streaming chunk formats and reasoning/text semantics,
consistent attachment mediaType handling, and more reliable reranking
via log-prob handling.

- Refactor
- Unified maxOutputTokens usage; removed per-call step caps and migrated
several tools to a unified inputSchema shape.

- Chores
- Upgraded AI SDK dependencies and bumped an internal dependency
version.

- Tests
- Updated mocks and tests to reference GPT-5 variants and new stream
formats.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Cargo.toml

@@ -93,7 +93,7 @@ tree-sitter-javascript = { version = "0.23" }
 tree-sitter-kotlin-ng  = { version = "1.1" }
 tree-sitter-python     = { version = "0.23" }
 tree-sitter-rust       = { version = "0.24" }
-tree-sitter-scala      = { version = "0.23" }
+tree-sitter-scala      = { version = "0.24" }
 tree-sitter-typescript = { version = "0.23" }
 uniffi                 = "0.29"
 url                    = { version = "2.5" }