Landing page section for COCOA (system graphs + blast radius) #7

Distribution follow-up from codellm-devkit/cocoa#1 (plan-2 stage 8). Add a COCOA section/page to codellm-devkit.info: the pitch (precise static system graphs for AI agents; provenance-tagged blast radius), the Online Boutique demo evidence (~25,000x token headline, estimate), install matrix pointer (cocoa's docs/INSTALL.md), and the graphify comparison (cocoa's docs/COMPARISON.md). Assets: demo.gif renders from cocoa's demo.tape (warm-cache protocol in the file).