get_channel_overview returns only first day's data instead of summing across date range #8

Bug Description

The get_channel_overview tool returns incorrect metrics when querying multi-day date ranges. It only returns data from the first day (possibly 0 if that day has no activity) instead of aggregating across all days in the range.

Root Cause

In src/utils/formatters/health.ts, the parseChannelOverview function uses data.rows[0] (first row only) instead of summing all rows:

const totalRow = data.rows[0] || []; // Bug: only uses first row

Since getChannelOverview queries with dimensions: 'day', YouTube returns one row per day. The current code discards all but the first day's data.

Reproduction

Query get_channel_overview for a date range where the first day has no activity but later days do:

get_channel_overview({ startDate: "2024-01-01", endDate: "2024-12-31" })

Expected: Aggregated metrics across all days (e.g., 9 views)
Actual: First day's metrics only (0 views)

Contrast with Working Implementation

get_engagement_metrics works correctly because it uses calculateMetricTotals in src/utils/transformers/analytics.ts, which properly sums all rows.

Proposed Fix

Sum additive metrics (views, estimatedMinutesWatched, subscribersGained) across all rows, and use view-weighted averaging for rate metrics (averageViewDuration, averageViewPercentage).