feat: Add requirements importer for multi-language dependency files (#126)

Implements package import functionality for:
- requirements.txt (Python/pip)
- package.json (Node.js/npm)
- Gemfile (Ruby/bundler)
- Cargo.toml (Rust/cargo)
- go.mod (Go modules)

Features:
- Auto-detection of requirements files
- Dry-run mode for preview
- Dev dependency support
- Unified CLI interface
- 50+ unit tests

Author: yaya1738

README_IMPORT.md

@@ -0,0 +1,235 @@
+# Cortex Import - Package Requirements Importer
+
+Import dependencies from various package manager requirement files.
+
+## Quick Start
+
+```bash
+# Import from a single file
+cortex import requirements.txt
+cortex import package.json
+
+# Import from all detected files
+cortex import --all
+
+# Preview what would be installed
+cortex import --dry-run requirements.txt
+
+# Include dev dependencies
+cortex import --dev package.json
+```
+
+## Supported File Formats
+
+| File | Package Manager | Language |
+|------|-----------------|----------|
+| `requirements.txt` | pip | Python |
+| `package.json` | npm | Node.js |
+| `Gemfile` | bundler | Ruby |
+| `Cargo.toml` | cargo | Rust |
+| `go.mod` | go | Go |
+
+## Commands
+
+### Import Single File
+
+```bash
+cortex import <file>
+
+# Examples:
+cortex import requirements.txt
+cortex import package.json
+cortex import Gemfile
+cortex import Cargo.toml
+cortex import go.mod
+```
+
+### Import All Detected Files
+
+```bash
+cortex import --all
+
+# From a specific directory
+cortex import --all --dir /path/to/project
+```
+
+### Detect Files Only
+
+```bash
+cortex import --detect
+
+# Output:
+# Detected requirements files:
+#   - requirements.txt
+#   - package.json
+```
+
+### Dry Run (Preview)
+
+```bash
+cortex import --dry-run requirements.txt
+
+# Output:
+# Parsing requirements.txt (pip)...
+# Dependencies (3):
+#   - flask (2.0.1)
+#   - requests (2.28.0)
+#   - django
+# Installing...
+# Success: [DRY RUN] Would install 3 packages via pip
+```
+
+### Include Dev Dependencies
+
+```bash
+cortex import --dev package.json
+```
+
+## Options
+
+| Option | Short | Description |
+|--------|-------|-------------|
+| `--all` | `-a` | Import from all detected files |
+| `--detect` | `-d` | Detect files without importing |
+| `--dry-run` | `-n` | Preview without installing |
+| `--dev` | | Include dev dependencies |
+| `--verbose` | `-v` | Show detailed output |
+| `--dir` | | Directory to search (default: `.`) |
+
+## File Format Examples
+
+### requirements.txt (Python)
+
+```txt
+flask==2.0.1
+requests>=2.28.0
+django~=4.0
+celery[redis]
+# Comments are ignored
+```
+
+Supported specifiers:
+- Exact: `package==1.0.0`
+- Range: `package>=1.0,<2.0`
+- Compatible: `package~=1.0`
+- Extras: `package[extra1,extra2]`
+- Environment markers: `package; python_version >= "3.8"`
+
+### package.json (Node.js)
+
+```json
+{
+  "dependencies": {
+    "express": "^4.18.0",
+    "lodash": "~4.17.21"
+  },
+  "devDependencies": {
+    "jest": "^29.0.0",
+    "eslint": "^8.0.0"
+  }
+}
+```
+
+### Gemfile (Ruby)
+
+```ruby
+source 'https://rubygems.org'
+
+gem 'rails', '7.0.0'
+gem 'pg', '>= 0.18', '< 2.0'
+
+group :development do
+  gem 'rubocop'
+end
+
+group :test do
+  gem 'rspec', '3.12.0'
+end
+```
+
+### Cargo.toml (Rust)
+
+```toml
+[package]
+name = "myproject"
+version = "0.1.0"
+
+[dependencies]
+serde = "1.0"
+tokio = { version = "1.28", features = ["full"] }
+
+[dev-dependencies]
+criterion = "0.5"
+```
+
+### go.mod (Go)
+
+```go
+module example.com/myproject
+
+go 1.21
+
+require (
+    github.com/gin-gonic/gin v1.9.1
+    github.com/spf13/cobra v1.7.0
+)
+```
+
+Indirect dependencies (marked with `// indirect`) are skipped.
+
+## Python API
+
+```python
+from cortex.requirements_importer import (
+    RequirementsImporter,
+    RequirementsParser,
+    PackageJsonParser,
+)
+
+# Create importer
+importer = RequirementsImporter(dry_run=True, verbose=True)
+
+# Detect files in current directory
+files = importer.detect_files('.')
+print(f"Found: {files}")
+
+# Parse a single file
+result = importer.parse_file('requirements.txt')
+print(f"Dependencies: {len(result.dependencies)}")
+print(f"Package manager: {result.package_manager.value}")
+
+# Install
+success, message = importer.install(result, include_dev=True)
+print(f"Install: {message}")
+
+# Get summary
+print(importer.summary())
+```
+
+## Exit Codes
+
+| Code | Description |
+|------|-------------|
+| 0 | Success |
+| 1 | Error (file not found, parse error, install failed) |
+
+## Requirements
+
+- Python 3.8+
+- Package managers must be installed for installation:
+  - pip (Python) - usually included with Python
+  - npm (Node.js) - install Node.js
+  - bundler (Ruby) - `gem install bundler`
+  - cargo (Rust) - install Rust via rustup
+  - go (Go) - install Go
+
+## Files
+
+- `cortex/requirements_importer.py` - Core implementation
+- `cortex/import_cli.py` - CLI commands
+- `tests/test_requirements_importer.py` - Unit tests (50+ tests)
+- `README_IMPORT.md` - This documentation
+
+## Related Issue
+
+- [#126 Package Import from Requirements Files](https://github.com/cortexlinux/cortex/issues/126)