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-kernel-display.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "bun:test";
-import { type KernelDisplayOutput, PythonKernel } from "$c/core/python-kernel";
+import { type KernelDisplayOutput, PythonKernel } from "$c/ipy/kernel";
 
 const renderDisplay = (
 	PythonKernel as unknown as {