fix(coding-agent): use valid JSON schema for submit_result when no output schema specified

Replace Type.Any() with Type.Object({}, { additionalProperties: true }) in the
submit_result tool's fallback data schema. Type.Any() serializes to
{"description": "..."} which lacks the required 'type' field for valid
JSON Schema. Strict providers (e.g. MiniMax, Cloud Code Assist) reject this
with 400 Unrecognized schema errors.

The fix produces {"type": "object", "additionalProperties": true, ...}
which conforms to JSON Schema draft 2020-12 while preserving the same
permissive acceptance of arbitrary structured output.

Fixes schema rejection observed with:
- MiniMax API (via zuccaro/bryce proxy)
- Cloud Code Assist (Claude) - related to #45

Co-authored-by: Cursor <cursoragent@cursor.com>

packages/coding-agent/src/tools/submit-result.ts

@@ -89,7 +89,7 @@ export class SubmitResultTool implements AgentTool<TObject, SubmitResultDetails>
 					...(normalizedSchema as object),
 					description: `Structured output matching the schema:\n${schemaHint}`,
 				})
-			: Type.Any({ description: "Structured JSON output (no schema specified)" });
+			: Type.Object({}, { additionalProperties: true, description: "Structured JSON output (no schema specified)" });
 
 		this.parameters = Type.Object({
 			data: Type.Optional(dataSchema),