chore(docs): remove 9 superseded one-time-analysis docs

Each of these reached completion and contributed its content to the
implementation; none has ongoing maintenance value. Recoverable via git
history if any future contributor needs the historical reasoning.

  - HANDOFF-TO-SONNET.md          session handoff from 2026-04-25, all
                                  tasks now landed
  - docs/IMPLEMENTATION-SPECS.md  work-order for container isolation +
                                  GNN training, both shipped
  - KATAGORIA_ECHO_INTEGRATION_ANALYSIS.md  "ALREADY FULLY INTEGRATED"
  - TYPELL_INTEGRATION_FEASIBILITY.md       "Already fully implemented"
  - JULIA_INTEGRATION_STRATEGY.md  pre-v2 strategy; impl supersedes it
  - ECHIDNA_COMPARISON_ANALYSIS.md superseded by OTHER_SYSTEMS_USP_PPA
  - docs/design/CHAPEL_METALAYER_ANALYSIS.md     pre-Chapel feasibility
  - docs/design/CHAPEL_PLUGGABILITY_DESIGN.md    Chapel now shipped
  - docs/design/ZIG_FFI_ANALYSIS.md              Zig FFI now shipped

https://claude.ai/code/session_01YPqu7gti4azBach6ZvpRFJ

Author: claude