Fix messages per day chart x-axis overflow

[staticpayload]

Summary

Fixes #18

The Problem

The "Messages per day" chart on the /stats page got stuck at March 2025 because the x-axis scale calculation couldn't handle the growing number of days of data.

Root Cause Analysis:

The previous bar width calculation:

bar_width = [(available_width - (total_days * bar_spacing)) / total_days, min_bar_width].max

When total_days grew large (e.g., 600+ days since community started):

• Formula produced negative or very small values
• .max would pick min_bar_width = 0.15
• But then: 600 * (0.15 + 0.05) = 120% width
• Result: Bars rendered outside the SVG, appearing "stuck"

The Solution

Replaced with adaptive scaling logic that:

1. Calculates target width per bar based on actual available space
2. When there's room (few days): Uses spacing for visual clarity
3. When space is tight (many days): Eliminates spacing first
4. Failsafe: Scales bar width proportionally to always fit

# Calculate bar width and spacing that actually fits
available_width = 100 - left_margin - right_margin
target_bar_width = available_width / total_days.to_f
min_bar_width = 0.1
max_bar_spacing = 0.05

if target_bar_width >= min_bar_width + max_bar_spacing
  # Plenty of room - use max spacing
  bar_spacing = max_bar_spacing
  bar_width = target_bar_width - bar_spacing
else
  # Tight on space - eliminate spacing and use minimum width
  bar_spacing = 0
  bar_width = [target_bar_width, min_bar_width].max

  # If still can't fit, scale everything down proportionally
  if bar_width * total_days > available_width
    bar_width = available_width / total_days.to_f
  end
end

Visual Result

Days	Before	After
~200	✅ Works	✅ Works
~400	⚠️ Starts overflowing	✅ Works
600+	❌ Completely broken	✅ Works (scales down)

The chart will now display all data correctly regardless of how many days of messages exist in the community.

Testing

• Chart renders correctly with current data volume
• Bar width scales proportionally as days increase
• No overflow beyond SVG boundaries
• X-axis labels remain readable (auto-spacing)

AI Disclosure

This PR was developed with AI assistance:

• Opus 4.5 for planning and code review
• GLM 4.7 for code execution
• GitHub PR review for quality assurance