fix(banner): move off gpt-image-1 before its Oct 23 shutdown

[ralyodio]

Closes #134 (thanks @Lakshya-0910).

• generate-banner now uses gpt-image-2.5-sunburst for both images/edits and images/generations; OPENAI_IMAGE_MODEL overrides.
• Verified against OpenAI with our key: both requests (1536x1024, quality=high) return 200 with b64_json.
• eslint, prettier, tsc --noEmit (apps/web) clean.

🤖 Generated with Claude Code

[github-actions]

ThreatCrush Security Scan

47 finding(s)

HIGH/CRITICAL: 4 | MEDIUM: 27 | LOW: 16

Severity	Rule	Location
HIGH	sh-eval-expansion	.githooks/pre-commit:33
HIGH	js-electron-node-integration	apps/desktop/src/main/window.ts:49
HIGH	sh-unquoted-expansion-destructive	apps/installer/scripts/install.sh:715
HIGH	sh-unquoted-expansion-destructive	apps/installer/scripts/install.sh:917
MEDIUM	sh-remote-script-execution	apps/installer/scripts/install.sh:691
MEDIUM	sh-remote-script-execution	apps/installer/scripts/install.sh:820
MEDIUM	sh-remote-script-execution	apps/installer/scripts/install.sh:822
MEDIUM	sh-remote-script-execution	apps/installer/scripts/install.sh:1078
MEDIUM	sh-remote-script-execution	apps/installer/scripts/install.sh:1080
MEDIUM	sh-remote-script-execution	apps/livekit/setup-livekit-server.sh:93
MEDIUM	sh-remote-script-execution	apps/turn/deploy-droplet.sh:62
MEDIUM	js-unescaped-html-sink	apps/web/src/app/blog/[slug]/page.tsx:48
MEDIUM	js-unescaped-html-sink	apps/web/src/app/blog/[slug]/page.tsx:73
MEDIUM	js-unescaped-html-sink	apps/web/src/app/c/[handle]/page.tsx:196
MEDIUM	js-open-redirect	apps/web/src/app/cli/authorize/consent.tsx:66
MEDIUM	js-unescaped-html-sink	apps/web/src/app/l/[joinCode]/page.tsx:129
MEDIUM	js-unescaped-html-sink	apps/web/src/app/l/[joinCode]/page.tsx:213
MEDIUM	js-unescaped-html-sink	apps/web/src/app/layout.tsx:141
MEDIUM	js-unescaped-html-sink	apps/web/src/app/live/page.tsx:145
MEDIUM	js-unescaped-html-sink	apps/web/src/app/page.tsx:123
MEDIUM	js-unescaped-html-sink	apps/web/src/app/pricing/page.tsx:286
MEDIUM	js-open-redirect	apps/web/src/app/pricing/UpgradeButton.tsx:50
MEDIUM	js-unescaped-html-sink	apps/web/src/app/u/[username]/page.tsx:282
MEDIUM	js-open-redirect	apps/web/src/hooks/useDesktopHandoff.ts:24
MEDIUM	redos-nested-quantifier	apps/web/src/lib/deliverable.ts:11
MEDIUM	js-unescaped-html-sink	apps/web/src/lib/player/player.ts:124
MEDIUM	js-unescaped-html-sink	apps/web/src/lib/player/player.ts:393
MEDIUM	js-unescaped-html-sink	apps/web/src/lib/player/player.ts:396
MEDIUM	js-unescaped-html-sink	apps/web/src/lib/player/player.ts:405
MEDIUM	js-unescaped-html-sink	apps/web/src/lib/player/player.ts:608
MEDIUM	sql-template-interpolation	packages/ai-core/src/prompts.ts:36
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:138
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:139
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:340
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:341
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:371
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:372
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:383
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:397
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:398
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:405
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:415
LOW	secret-generic-credential	apps/desktop/src/main/agent-cli/commands.test.ts:416
LOW	secret-generic-credential	apps/livekit/fly.toml:12
LOW	secret-generic-credential	apps/turn/fly.toml:11
LOW	secret-generic-credential	docs/API.md:747
LOW	secret-generic-credential	docs/API.md:753

Snippets are redacted; ThreatCrush never prints matched credential material.