feat: Add npx CLI package for Copilot token usage analysis

[Copilot]

Standalone CLI (copilot-token-tracker-cli) publishable to npmjs.org that reuses the extension's session discovery, parsing, token estimation, maturity scoring, and usage analysis modules without modifying them.

npx copilot-token-tracker-cli stats --verbose
npx copilot-token-tracker-cli usage --models --cost
npx copilot-token-tracker-cli env
npx copilot-token-tracker-cli fluency --tips

CLI Package (cli/)

• stats — Files, sessions, chat turns, tokens; breakdown by editor source
• usage — Token usage by period (today/month/last month/30d) with optional per-model and cost breakdowns
• environmental — CO₂, water, tree-offset estimates with real-world context comparisons
• fluency — Copilot Fluency Score across all 6 categories with optional improvement tips
• VS Code API stubbed via cli/src/vscode-stub.ts so sessionDiscovery.ts and opencode.ts imports resolve cleanly
• OpenCode DB virtual paths (opencode.db#ses_<id>) handled via dedicated statSessionFile() helper
• esbuild bundles everything into a single dist/cli.js (~415KB) targeting Node 18+

Root integration

• Added cli:build, cli:stats, cli:usage, cli:environmental, cli:fluency, cli npm scripts
• Excluded cli/ from root tsconfig.json to avoid rootDir conflicts

Workflows

• cli-build.yml — Validates build + all commands on Node 18/20/22, triggered on changes to cli/ or shared source modules
• cli-publish.yml — workflow_dispatch with version bump selector (patch/minor/major) and dry-run option; requires NPM_TOKEN secret