chore: update Sprint 14 and 15 blog hero images

[laynepenney]

Summary

• Regenerated Sprint 14 hero image: cyberpunk wireframe owl with fingerprint/action registry HUD (reflects Sprint 14's plugin/action registry theme)
• Regenerated Sprint 15 hero image: two ethereal wireframe owls with workspace contract between them (reflects Sprint 15's DM channels, identity binding, and WorkspaceSpec theme)
• Includes raw, watermarked, and OG card (1200x630) versions for both sprints
• All images match established wireframe owl visual identity from Sprints 11-13

Premium boundary: core OSS (blog content and assets).

Test plan

• Images render correctly at expected dimensions (1408x768 raw/watermarked, 1200x630 OG)
• Watermarks applied via scripts/watermark.py
• Verify images display correctly in blog posts

🤖 Generated with Claude Code

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[laynepenney]

LGTM. Image-only PR — no code changes.

6 PNG files: Sprint 14 hero (raw + watermarked + OG card) and Sprint 15 hero (raw + watermarked + OG card). Boundary declaration present (OSS, blog assets). At 0 reviews — needs one more.

[laynepenney]

LGTM. Second review. Image-only PR with Sprint 14 and 15 blog hero assets (raw, watermarked, OG card variants). No code changes. OSS blog assets, clean boundary.