refactor: decompose init.ts action handler into phase functions

[dean0x]

Problem

The init.ts action handler (src/cli/commands/init.ts:112-631) is 520+ lines with 10+ responsibilities:

• Version detection
• Scope determination (user/local)
• Interactive prompts (TTY handling)
• Plugin discovery and installation
• Registry updates
• Hook installation (memory, ambient, etc.)
• Working memory bootstrap
• Error handling and user feedback

Scope

This file is monolithic and violates single-responsibility principle. Extracting just 2-3 small blocks is insufficient. A proper refactor requires:

1. Phase functions - Decompose into ~5-7 phase handlers:

   • detectVersion() - Package version loading
   • determineScope() - User/local scope selection
   • selectPlugins() - Interactive plugin selection
   • installPlugins() - Plugin installation orchestration
   • setupHooks() - Memory and ambient hook installation
   • bootstrapMemory() - Working memory initialization
   • concludeInstallation() - Summary and next steps

2. Helper utilities - Extract reusable patterns:

   • Registry update logic
   • File system operations
   • Error recovery and logging

3. Type safety - Define phase-to-phase contracts with Result types

Risk Assessment

• Risk Level: HIGH
• Why: The file is working and well-tested. Any refactor touches core installation logic
• Mitigation: Comprehensive test coverage already exists; refactor can be validated via existing test suite

Testing Strategy

• Keep all existing tests passing (no behavior changes)
• Add unit tests for new phase functions
• Integration test full installation flow end-to-end

Acceptance Criteria

• Handler decomposed into phase functions
• Phase functions are <100 lines each
• All existing tests pass
• New tests cover phase boundaries
• Line count reduced from 520 to ~300-350 in main handler

Priority

Low - works well currently. Defer to post-v1.0.0 dedicated refactoring effort.