style(deps): migrated from Prettier to Biome and updated formatting rules

- Removed Prettier configuration files (.prettierignore and .prettierrc) and migrated formatting to Biome.
- Updated Biome configuration from version 2.3.11 to 2.3.12 and changed arrowParentheses rule from 'always' to 'asNeeded'.
- Pinned @biomejs/biome dependency to exact version 2.3.12 in package.json and bun.lock.
- Applied consistent arrow function formatting across 489 files by removing unnecessary parentheses around single parameters.
- Removed blank lines after comment blocks and reorganized imports for consistency across the codebase.

packages/coding-agent/test/core/python-executor-timeout.test.ts

@@ -21,7 +21,7 @@ describe("executePythonWithKernel cancellation", () => {
 	it("annotates timeouts when cancelled", async () => {
 		const kernel = new FakeKernel(
 			{ status: "ok", cancelled: true, timedOut: true, stdinRequested: false },
-			(options) => {
+			options => {
 				options?.onChunk?.("tick\n");
 			},
 		);