[Core] Add feedback text to evaluation dimensions

[SaharPak]

The evaluator in packages/core/src/evaluator/index.ts returns empty strings for every dimension's feedback field:

feedback: '',  // This is empty everywhere

Add meaningful feedback text for each scoring function. Examples:

• Shipped Evidence (score 1): 'No evidence of shipped work found. Add verbs like Built, Deployed, Launched with specific outcomes.'
• Shipped Evidence (score 4): 'Strong shipping signals found. Consider adding scale indicators (users served, uptime, etc.)'
• Quantified Impact (score 2): 'Only {n} metrics found. Aim for at least one number per bullet point.'
• Keyword Match (score 3): 'Matched {n}/{total} JD keywords. Missing: {list of top 5 missing keywords}'

Each scoring function should return both the score and a feedback string. This is the most important user-facing improvement.