Add Shell Auto-Completion Support

Description

Add shell auto-completion scripts for bash, zsh, and fish to improve developer experience and command discoverability. Users should be able to tab-complete commands, options, testset names, solution names, and other context-aware arguments.

Features

Command Completion:

```bash
polyman gen → polyman generate
polyman rem → polyman remote
```

Option Completion:

```bash
polyman generate --
→ --all --testset --group --index

polyman remote push --
→ --all --solutions --checker --validator --tests
```

Context-Aware Completion:

```bash
# Complete testset names from Config.json
polyman generate -t
→ tests samples pretests

# Complete solution names from Config.json
polyman run
→ main correct2 wa-solution tle-solution

# Complete generator names
polyman generate -t tests -g
→ samples main stress
```

Implementation Approach
Using commander-completion

```ts
import completion from 'commander-completion';

program
.command('completion')
.description('Generate shell completion script')
.action(() => {
completion(program);
});
```

**Success Criteria**

- Completion works for all shells (bash, zsh, fish)
- Static command/option completion works
- Dynamic completion reads Config.json
- Handles missing Config.json gracefully (fallback to static completion)
- Installation instructions in README
- Auto-suggest during npm install -g polyman-cli