feat: Make plugin output directory name configurable

[obie]

Summary

• Adds a new pluginName config field to .praxis/config.json (defaults to "praxis" for backward compatibility)
• Threads the value through PraxisConfig → RoleCompiler → PluginRegistry → ClaudeCodePlugin
• The Claude Code plugin now writes to plugins/{pluginName}/agents/ instead of hardcoded plugins/praxis/agents/

This allows projects like Canon to set "pluginName": "canon" in their config and get output written to plugins/canon/agents/.

Files changed

• src/core/config.ts — new pluginName field in RawConfig, DEFAULT_CONFIG, and PraxisConfig getter
• src/compiler/plugins/types.ts — added pluginName to PluginOptions interface
• src/compiler/plugins/claude-code.ts — uses pluginName from options instead of hardcoded "praxis"
• src/compiler/plugin-registry.ts — passes pluginName through to plugin constructors
• src/compiler/role-compiler.ts — passes config.pluginName to resolvePlugins

Test plan

• npm run build compiles successfully
• All existing tests pass (156/157 — 1 pre-existing flaky watcher test unrelated to this change)
• Verify with a Canon project that "pluginName": "canon" outputs to plugins/canon/agents/