Bug: duplicate Fabric version validation - _verifyFabricVersion is unreachable dead code

## Summary

In `src/commands/validate/index.ts`, two separate methods validate the **exact same condition** - whether `fabricVersion >= 2.0.0`:

1. **`_validateFabricVersion()`** (line 153) - emits a `CRITICAL` error -> calls `process.exit(1)` immediately
2. 2. **`_verifyFabricVersion()`** (line 562) - emits a regular `ERROR` -> just adds to error list
Since `_validateFabricVersion` is called first (line 118 in `validate()`) and exits the process on failure, `_verifyFabricVersion` (called at line 150) is **unreachable dead code** when the version check fails.

## Steps to Reproduce

1. Set `fabricVersion` to `"1.4.0"` in a `fablo-config.json`
2. 2. Run `fablo validate`
3. 3. Observe that `_validateFabricVersion` fires first and exits with `process.exit(1)`
4. 4. `_verifyFabricVersion` never executes
## Expected Behavior

There should be a single, clear Fabric version validation - not two methods checking the same thing with different severity levels.

## Proposed Fix

Remove the redundant `_verifyFabricVersion` method (lines 562-567) and its call (line 150). The existing `_validateFabricVersion` already handles this correctly with a CRITICAL exit.

Happy to open a PR for this fix.