chore(docs): consolidate documentation, drop dead files

Cleanup
- Remove src/backend/Dockerfile.legacy and
  src/frontend/flask_app/Dockerfile.legacy (history is in git, build
  uses the new uv-based root Dockerfile / Dockerfile.frontend).
- Remove src/frontend/flask_app/verify_i18n.py (had hardcoded paths
  pointing at the old client/ tree).

Group docs/
- New docs/README.md indexes everything in one place.
- New docs/architecture/STATO_PROGETTO.md: snapshot of what works in
  V2.0.0 (inherited V1.0.7 features, rev04 Phase 1 stations,
  worker scaling, src/ restructure, test status, stack, decisions).
- New docs/architecture/ROADMAP.md: what's next — Phases 2-7 of the
  rev04 migration with status, open client decisions (D-0.1 through
  D-0.10), tech debt and time estimates for M1 / M2.
- Move PIANO_IMPLEMENTAZIONE.md (90KB V1.0.0 plan) to
  docs/archive/2026-02-06-piano-implementazione-v1.md (historical).
- Move Schema sviluppo SW TieFlow_rev04-2026.docx to docs/specs/
  with ISO date filename so the customer spec is now tracked.
- Move src/frontend/flask_app/I18N_SETUP.md to docs/I18N_SETUP.md
  and rewrite paths to the new src/frontend/flask_app/ tree.

.dockerignore: simplified now that legacy Dockerfiles are gone;
docs/ stays excluded from the build context.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/backend/Dockerfile.legacy

@@ -1,26 +0,0 @@
-FROM python:3.11-slim
-
-# Installa dipendenze sistema per WeasyPrint
-RUN apt-get update && apt-get install -y --no-install-recommends \
-    libpango-1.0-0 \
-    libpangocairo-1.0-0 \
-    libcairo2 \
-    libgdk-pixbuf-2.0-0 \
-    libffi-dev \
-    shared-mime-info \
-    && rm -rf /var/lib/apt/lists/*
-
-WORKDIR /app
-
-COPY requirements.txt .
-RUN pip install --no-cache-dir -r requirements.txt
-
-COPY . .
-
-# Crea directory uploads
-RUN mkdir -p uploads/images uploads/pdfs uploads/logos uploads/reports
-
-EXPOSE 8000
-
-# Entry point: Alembic upgrade + Uvicorn
-CMD ["sh", "-c", "alembic -c migrations/alembic.ini upgrade head && uvicorn main:app --host 0.0.0.0 --port 8000 --workers 4 --proxy-headers --forwarded-allow-ips='*'"]