Summary

This PR adds thorough documentation covering the entire codebase, every module, formula, and design decision explained in plain English alongside the math.

• README.md : Updated with scenario table, links to all docs, quick start
• ARCHITECTURE.md : Full directory map, module dependencies, two-version comparison (draft vs. active fast fading), global parameter table
• FAST_FADING_PIPELINE.md : The complete 12-step 3GPP TR 38.901 GBSM process with formula derivations, code references, and a documented list of known bugs/TODOs
• PATHLOSS_AND_LOS.md : Every path loss formula (RMa, UMa, UMi, InH, InF) with LOS probability models and the V2I baseline models in ChannelModel.py
• ADDITIONAL_COMPONENTS.md :All optional extensions: spatial consistency, blockage model B, oxygen absorption, dual mobility, UT rotation, large bandwidth, ATOA, CDL-A/B/C/D/E, Rician fading (Rice class)
• PHYSICAL_TO_APPLICATION.md :The latency/PRR simulator with 5G NR numerology background, resource scheduling logic, and link-level assumption checklist

Test plan

• [ x] Verify all file links in README.md resolve correctly
• Check that formula notation matches 3GPP TR 38.901 V17.0.0 tables
• Confirm no existing source files were modified