docs: refine skill delegation section for conciseness and clarity

[avoidwork]

Description

Refinements to the SKILL DELEGATION section in the system prompt. Tightened language for conciseness and clarity without changing the underlying delegation model or behavior.

Type of Change

• Documentation update

Testing

N/A — prompt-only change, no code affected.

Coverage

• 100% line coverage maintained

Checklist

• npm run lint passes
• Tests pass with 100% line coverage
• No forbidden patterns used
• Conventional Commit style applied

Changes

• Step 1: Changed 'Read the target skill's SKILL.md first' to 'when needed' — added conditional skip if contract already known from context.
• Step 2: Simplified parameter gathering language — removed 'confirm if genuinely ambiguous' in favor of 'proceed — only ask when zero viable paths forward.'
• Step 4: Added 'When the output of one step clearly implies the next, proceed without hesitation' to discourage unnecessary pausing.
• Step 5: Removed 'Never drop the chain' — the principle is already implicit.
• When to delegate: Removed verbose justifications, kept core decision criteria.