refactor: restructure metadata files for context efficiency

- Shrink global AGENTS.md: 153 → 56 lines (−63%)
  Removed: git workflow, TDD, overthinking guards, code style, reasoning protocol
  Kept: personality, git basics, thinking levels, general principles, backend
- Create project AGENTS.md: 71 lines
  Added: stack/commands, GitHub Flow git workflow, Conventional Commits,
  TDD (Python-specific), quality gates, debug verification
- Trim CONVENTIONS.md: 161 → 68 lines (−58%)
  Removed: verbose examples, redundant unit convention section,
  lengthy SpectrumComponent code example
- Delete DEVELOPMENT.md: 238 lines → 0 (migrated to AGENTS.md)
  Setup/release checklist removed (not agent concerns)
  Git workflow, TDD, quality gates, notebook QC, debug verification
  all migrated to AGENTS.md
- Update README.md project structure
Total per-session metadata: 552 → 195 lines (−65%)

README.md

@@ -75,10 +75,13 @@ beta_shape_pnpi/
 │   ├── test_fitter.py           # Curve fitter tests
 │   ├── test_cw_extractor.py     # C(W) extraction tests
 │   └── test_nuclear_data.py     # paceENSDF + JSON input tests (23 tests)
-└── data/
-    ├── exchange_coeff.csv         # Tabulated coefficients for X(Z,W), Z=2..120
-    └── custom_input_example.json  # Sample JSON input file
+├── data/
+│   ├── exchange_coeff.csv         # Tabulated coefficients for X(Z,W), Z=2..120
+│   └── custom_input_example.json  # Sample JSON input file
 ├── output/                      # Test run outputs (gitignored except .gitkeep)
+├── AGENTS.md                    # Agent instructions: stack, git workflow, TDD, quality gates
+├── CONVENTIONS.md               # Physics conventions: natural units, energy representation, component design
+├── TODO.md                      # Development roadmap
 ```
 
 ______________________________________________________________________