docs: add Russian project report notebook (notebooks/report.ipynb)

Runnable end-to-end report combining narrative, code, and inline figures:
data and .chord format, transformer working principle, two-stage training
curves, perplexity (3.58 -> 2.15), distribution-shift plot with a reading
legend, qualitative examples, and a generation demo. Written in a
first-person student voice.

- CLAUDE.md: report is now a Jupyter notebook; GOST formatting dropped
- requirements.txt: add nbconvert + ipykernel (optional, for the notebook)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

requirements.txt

@@ -15,5 +15,9 @@ matplotlib==3.10.9
 # Web UI (optional — only needed for app.py)
 gradio==6.16.0
 
+# Report notebook (optional — only needed to run notebooks/report.ipynb)
+nbconvert==7.17.1
+ipykernel==7.2.0
+
 # Testing
 pytest==9.0.3