feat: monorepo — each command as an independent workspace package

[Copilot]

Splits the single-package repo into a Yarn workspaces monorepo where every command is an independently versioned/publishable package.

Layout

packages/
├── core/           @fsr/core          shared utils, parsers, UI, running, plugins, cache
├── cli/            fscr               bin entrypoint
├── cmd-branch/     @fsr/cmd-branch
├── cmd-commit/     @fsr/cmd-commit
├── cmd-start/      @fsr/cmd-start     start / list / scripts
├── cmd-run/        @fsr/cmd-run       run / run-s / run-p
├── cmd-upgrade/    @fsr/cmd-upgrade
├── cmd-bump/       @fsr/cmd-bump
├── cmd-encryption/ @fsr/cmd-encryption
├── cmd-generate/   @fsr/cmd-generate
├── cmd-doctor/     @fsr/cmd-doctor
├── cmd-completion/ @fsr/cmd-completion
├── cmd-greet/      @fsr/cmd-greet
├── cmd-clear/      @fsr/cmd-clear
└── cmd-plugins/    @fsr/cmd-plugins

Key changes

• Root package.json: private: true, workspaces: ["packages/*"]; existing deps hoisted to root
• @fsr/core: all lib/ internals extracted; exports a flat public API (fsrLog, parseScriptFile, loadPlugins, etc.)
• Command packages: each exports a command definition object { cmd, desc, builder?, handler, examples?, menu? } (arrays for multi-sub-command packages); all cross-package imports use @fsr/core named exports
• packages/cli: publishable fscr package; assembles COMMANDS from @fsr/cmd-* imports
• Root index.js: unchanged public behaviour — now delegates entirely to package imports
• vitest.config.js: path aliases for all @fsr/* packages + esbuild JSX config for .js files containing JSX
• scripts/bun.build.mjs: alias map updated to resolve @fsr/* during bundling
• lib/: preserved untouched; test files outside tests/index.test.js still import from it directly