[No Jira] - add browser support section to README

[wjames111]

Description

Updates readme with current targeted browser support and usage based off of this document.

Testing

• Go to ...
• Do ...
• Check that ...

Checklist:

• I have given my PR a title with the format "MPDX-(JIRA#) (summary sentence max 80 chars)"
• I have applied the appropriate labels (Add the label "Preview" to automatically create a preview environment)
• I have run the Claude Code /pr-review command locally and fixed any relevant suggestions
• I have requested a review from another person on the project
• I have tested my changes in preview or in staging
• I have cleaned up my commit history

[github-actions]

Bundle sizes [mpdx-react]

Compared against 2d5c268

No significant changes found

[wjames111]

Multi-Agent Review Summary

Verdict: APPROVED WITH SUGGESTIONS
Risk: 0/10 (LOW) — documentation-only change
Agents: Architecture, Testing & Quality, Standards (3 of 6, smart-selected)

Findings

• 0 Critical / 0 High / 0 Important
• 1 Medium (severity 5.0) — next.mpdx.org URL is not defined in the README's Environments section
• 4 Suggestions (severity < 5.0) — table layout, date staleness, rounding footnote, (not set) explanation

Verified Facts

• Next.js version (^15.0.3) matches the "Next.js 15" claim
• No browserslist in package.json, no .browserslistrc, no overrides in next.config.ts
• Listed browser targets (Chrome 64+, Edge 79+, Firefox 67+, Safari 12+, Opera 51+) match Next.js 15's documented Browserslist defaults exactly
• Markdown heading level and table syntax are valid GFM
• Browser shares sum to 99.8% (rounding-consistent)
• Date range (Apr 8 – May 5, 2026) is in the past relative to today

No Blockers

This PR can ship as-is. The Medium finding (next.mpdx.org clarification) and Suggestions are polish — address in this PR or follow up later. Suggestions cannot be dismissed via /dismiss because they are below severity 7.0; they are informational only.

[wjames111]

[Suggestion] **`(not set)` row is unexplained.**

21.9% is a large bucket without context. A brief parenthetical — e.g., "GA4's bucket for sessions where the browser can't be identified (privacy extensions, bots, embedded webviews)" — would aid readers who aren't familiar with GA terminology.

Flagged by: Architecture Agent + Testing Agent

[github-actions]

AI Review Auto-Approval

Risk Level: LOW (0/10)
Verdict: APPROVED_WITH_SUGGESTIONS (suggestions posted, no blockers)

This PR was auto-approved because:

• The multi-agent AI review determined it is low risk
• No blocking issues were found
• All suggestions have been posted as review comments for the developer to consider

If you believe this PR needs human review, dismiss this approval and request a review manually.

[github-actions]

Preview branch generated at https://add-browser-support-readme.d3dytjb8adxkk5.amplifyapp.com