GLSP-1682: Group packages and set up the consolidated pnpm workspace

[tortmayr]

Turn the merged client/server/dev sources into a single, self-bootstrapping monorepo that builds, lints, and tests from the root.

• Group the merged packages by framework layer, using git renames so per-file history is preserved across the move: packages/common/protocol (shared between client and server), packages/client/{client,glsp-sprotty} and packages/server/{graph,layout-elk,server,server-mcp}
• Add the root workspace configuration: pnpm-workspace.yaml (globbing dev-packages/, packages//, examples/, with the unioned hoist, override, build-allow and release-age settings), the root package.json with merged scripts (including test:e2e for the CLI end-to-end suite) and in-workspace dev tooling, and the TypeScript project graph
• Add the shared lint/format/test configs: one path-scoped ESLint flat config carrying the common, client and server import rules, Prettier config, and a Vitest config that globs every package's specs
• Align internals for the grouped layout: fix the example -> package TS reference depths and switch the remaining next protocol deps to workspace:*
• Compile each package's specs as part of its own tsconfig instead of a separate tsconfig.test.json project, and exclude the emitted .spec./test output from the published tarball via files. This keeps decorator transpilation working for specs without a dedicated test tsconfig and independent of the test runner's tsconfig resolution
• Consolidate the example run/dev scripts: fold the standalone launcher into a single start.mts, default the workflow server to WebSocket with matching start/start:socket scripts, and drop the --external-server bundle-path option
• Adapt the glsp CLI to the consolidated structure: the repo commands address the client/server examples inside the glsp-core checkout, releng prepare maintains the component-grouped changelog layout, and package metadata is fixed up for the workspace. Make the workspace-resolution spec hermetic (it depended on /tmp contents)
• Add the consolidated CHANGELOG: releases group entries by component (Client / Server / Dev Packages); everything up to and including v2.8.0 is the merged history of the source repositories, v2.9.0 will be the first monorepo release
• Add the GitHub Actions setup: CI (build, test, lint, coverage) and CodeQL workflows plus issue/PR templates, with a lint:ci script that emits the JSON report the CI lint summary renders
• Add the canonical EPL-2.0 project docs (LICENSE, CONTRIBUTING, SECURITY, CODE_OF_CONDUCT), a consolidated README, the shared .vscode setup, and the AI agent metadata (AGENTS.md, CLAUDE.md, skills)

Part of: eclipse-glsp/glsp#1682

[tortmayr]

Still missing (will be handled in follow-up):

• CI for release flow
• CI for e2e tests
• Live deployment
• Planned integration of glsp-playwright directly