[roadmap] agent-loop: skeleton extraction for context offload — compress read files to signatures

[sam-fakhreddine]

From caliber-ai/ai-setup assessment (code-analysis.ts extractSkeletonIndentBased + compressContent). When context fills, compress already-read source files to signatures/imports/types only (indent-based strategy fits Python). Priority scoring for what stays full-fat: import fan-in + git frequency beats most-recently-touched. Direct implementation path for #71.