feat: update search for V2 API modes

[marc-rutzou]

Summary

• Add --mode flag to select search tier: instant, classic (default), or agentic
• Add --offset flag for pagination (instant/classic)
• Update API endpoint from /collections/{id}/search to /collections/{id}/search/{mode}
• Update result rendering for V2 response format (relevance_score, airweave_system_metadata, breadcrumbs, web_url)

Test plan

• Verify airweave search "query" uses classic mode by default
• Verify airweave search "query" --mode instant hits the instant endpoint
• Verify airweave search "query" --mode agentic hits the agentic endpoint
• Verify --offset is sent for instant/classic but not agentic
• Verify --json output matches V2 response schema
• Verify interactive result panels show breadcrumbs and correct score

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