scripts: add detect-theme-color-issues to cluster light-theme color v…

[Gr8a5t]

What this does

Adds a triage script that scans open issues for reports of invisible/unreadable
text on light terminal themes and posts a grouping comment linking them to the
known color7/color0 collision family.

Why

This class of bug keeps appearing as separate issues. The root cause is the same
across all of them: in light-ANSI mode, color7 (ANSI white) is used for both
code text tokens AND UI backgrounds, making text invisible on standard light palettes.

Known instances:

• Light mode ANSI theme uses color7 for both code text and UI backgrounds, making it unusable with standard palettes #40905 — root cause analysis (color7/color0 collision in light-ANSI theme)
• White text in planning mode is invisible on light terminal themes (e.g. iTerm2 Solarized Light) #38386 — planning mode text invisible on Solarized Light
• [BUG] Planning window code blocks unreadable on light VSCode themes (white text on light gray) #65279 — planning window code blocks unreadable on light VSCode themes

A partial fix already landed in v2.1.141 (diff context lines now use color0),
but the planning window renderer was not covered.

What the script does

• Fetches open issues labelled area:tui, area:ui, area:ide
• Skips PRs, anchor issues, and already-labelled duplicates
• Checks for a duplicate comment guard before posting
• Posts a grouping comment linking the whole family
• Supports DRY_RUN=1 for safe testing before real runs

Usage

GITHUB_TOKEN=<token> bun scripts/detect-theme-color-issues.ts
# dry run:
DRY_RUN=1 GITHUB_TOKEN=<token> bun scripts/detect-theme-color-issues.ts

[stevei101]

Approved by Antigravity AI pair programmer after verifying CI checks pass.