feat(node): Add CLI configuration validation for early error detection

[gap-editor]

Description

Adds comprehensive CLI configuration validation that runs before node services start. This prevents invalid or dangerous configurations from causing runtime failures or consensus issues.

Key Changes

Added Cli::validate() method that performs critical checks:

• Prevents zero values for grandpa_justification_period and kate_max_cells_size
• Enforces upper bounds on kate_max_cells_size (≤10,000) to prevent resource exhaustion
• Blocks --unsafe-da-sync + --validator combination (critical for consensus safety)
• Warns when Kate RPC metrics are enabled without Kate RPC

Integrated validation into startup flow (command.rs):

• Validation runs immediately after CLI parsing, before any services initialize
• Provides clear, actionable error messages for misconfigurations
• Fails fast to prevent silent operational failures

Why This Matters

Previously, invalid configurations could:

• Cause validators to skip data availability checks (consensus violation)
• Lead to finalization failures from zero-value parameters
• Enable DoS attacks via oversized RPC requests
• Produce errors hours after startup, making debugging difficult