refactor(coding-agent): flattened directory structure, eliminated core/ folder

- Eliminated core/ directory (252 files, 23 subdirs → distributed)
- Reduced max nesting from 9 levels to 5 levels
- Promoted tool subdirs to top level: exa/, lsp/, patch/, task/, web/
- Merged web-scrapers/ + web-search/ into web/{scrapers,search}/
- Flattened modes/interactive/ to modes/
- Split execution/ into: ipy/ (python), exec/ (bash), ssh/
- Renamed ipy/python-*.ts to ipy/*.ts (executor, kernel, etc.)
- Flattened cursor/exec-bridge.ts to cursor.ts
- Created logical groupings: config/, session/, extensibility/, export/
- Updated all imports across 500+ files

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

@@ -1,7 +1,7 @@
 import { afterEach, describe, expect, it, vi } from "bun:test";
-import { disposeAllKernelSessions, executePython } from "$c/core/python-executor";
-import type { KernelExecuteResult } from "$c/core/python-kernel";
-import * as pythonKernel from "$c/core/python-kernel";
+import { disposeAllKernelSessions, executePython } from "$c/ipy/executor";
+import type { KernelExecuteResult } from "$c/ipy/kernel";
+import * as pythonKernel from "$c/ipy/kernel";
 
 class FakeKernel {
 	execute = vi.fn(async () => this.result);