feat: implement package manager (Enhancement #2)

Adds Cargo-style dependency management for Ephapax projects.

Features:
- Manifest parsing (ephapax.toml) with TOML validation
- Dependency resolution using backtracking algorithm
- Local package registry (~/.ephapax/registry/)
- Version constraint satisfaction (SemVer)
- Transitive dependency resolution
- Mode-specific dependencies (affine/linear)
- CLI commands: init, install, search, list

New crate: ephapax-package (4 modules, 875 lines, 14 tests)
- manifest.rs: TOML parsing and validation
- registry.rs: Local package storage and indexing
- resolver.rs: Dependency resolution with backtracking
- lib.rs: Public API

CLI integration:
- ephapax package init <name>: Initialize new projects
- ephapax package install: Install from manifest
- ephapax package search <query>: Search packages
- ephapax package list: List installed packages

Testing:
- All 14 unit tests passing
- Integration test verified (init, manifest editing)

Documentation:
- docs/PACKAGE-MANAGER.md (complete guide)
- ENHANCEMENTS-STATUS.md updated (40% complete, 2/5 done)

Future enhancements:
- Phase 2: Remote registry (publish/download from central repo)
- Phase 3: Module import syntax in language
- Phase 4: Lockfile generation (ephapax.lock)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Jonathan D.A. Jewell

Cargo.lock

@@ -16,6 +16,7 @@ members = [
     "src/ephapax-cli",
     "src/ephapax-stdlib",
     "src/ephapax-lsp",
+    "src/ephapax-package",
     # "src/ephapax-vram-cache",  # Disabled: requires ephapax-proven repo
 ]
 
@@ -42,6 +43,7 @@ ephapax-interp = { path = "src/ephapax-interp" }
 ephapax-repl = { path = "src/ephapax-repl" }
 ephapax-stdlib = { path = "src/ephapax-stdlib" }
 ephapax-lsp = { path = "src/ephapax-lsp" }
+ephapax-package = { path = "src/ephapax-package" }
 ephapax-vram-cache = { path = "src/ephapax-vram-cache" }
 
 # External dependencies

Cargo.toml

@@ -1,7 +1,7 @@
 # Ephapax Enhancement Suite - Implementation Status
 
 **Date**: 2026-02-07
-**Overall Completion**: 20% (1/5 enhancements completed)
+**Overall Completion**: 40% (2/5 enhancements completed)
 
 This document tracks the implementation status of the 5 optional enhancements planned for Ephapax after reaching 100% core language completion.
 
@@ -110,12 +110,58 @@ ephapax compile test.eph --debug --mode linear
 
 ---
 
-## Enhancement #2: Package Manager ⏳ NOT STARTED
+## Enhancement #2: Package Manager ✅ COMPLETED
 
 **Priority**: 2
-**Status**: Planned
-**Completion**: 0%
-**Effort**: 2-3 weeks
+**Status**: Complete
+**Completion**: 100%
+**Effort**: ~4 hours (implemented 2026-02-07)
+
+### What Was Implemented
+
+#### ✅ Core Features
+- **Manifest Parsing**: Full `ephapax.toml` support with validation
+- **Local Registry**: Package storage in `~/.ephapax/registry/`
+- **Dependency Resolution**: Backtracking algorithm with SemVer constraints
+- **Version Selection**: Automatic latest compatible version selection
+- **Transitive Dependencies**: Recursive dependency tree resolution
+- **Mode-Specific Dependencies**: Support for `mode = "affine"` specification
+
+#### ✅ CLI Commands
+- `ephapax package init <name>` - Initialize new projects
+- `ephapax package install` - Install from manifest
+- `ephapax package search <query>` - Search local registry
+- `ephapax package list` - List installed packages
+
+#### ✅ New Crate: `ephapax-package`
+**Modules**:
+- `manifest.rs` - TOML parsing and validation (275 lines)
+- `registry.rs` - Local package storage (280 lines)
+- `resolver.rs` - Dependency resolution (230 lines)
+- `lib.rs` - Public API (90 lines)
+
+**Tests**: 14 unit tests covering:
+- Manifest parsing (valid/invalid cases)
+- Dependency specifications (simple, detailed, path, git)
+- Registry operations (install, search, versions)
+- Resolution (simple, transitive, version selection)
+
+### What Remains (Future Enhancements)
+
+#### ⏳ Phase 2: Remote Registry
+- HTTP API for package upload/download
+- Authentication with API tokens
+- `ephapax package publish` command
+- Central package repository
+
+#### ⏳ Phase 3: Module Import Syntax
+- Parser: Add `import` statement
+- Type checker: Resolve module paths
+- Codegen: Link multiple modules
+
+#### ⏳ Phase 4: Lockfile Generation
+- Generate `ephapax.lock` for reproducibility
+- Pin exact dependency versions
 
 ### Design