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-display.test.ts

@@ -30,7 +30,7 @@ describe("executePythonWithKernel display outputs", () => {
 
 		const kernel = new FakeKernel(
 			{ status: "ok", cancelled: false, timedOut: false, stdinRequested: false },
-			async (options) => {
+			async options => {
 				if (!options?.onDisplay) return;
 				for (const output of outputs) {
 					await options.onDisplay(output);