DFPY-79: Prepare 4.5 release readiness

[sidmohan0]

Summary

• Add a dedicated 4.5 release-readiness page covering release positioning, version alignment, final checklist gates, German regex behavior, optional OCR/Spark stance, telemetry defaults, and the v5 boundary.
• Add 4.5.0 unreleased changelog content and wire the release-readiness page into the docs navigation/planning docs.
• Teach the release changelog generator to emit 4.5-specific stable release notes when the release workflow publishes 4.5.0.

Verification

• .venv312/bin/pre-commit run --files CHANGELOG.MD docs/contributing.rst docs/index.rst docs/planning-history.rst docs/roadmap.rst docs/v45-release-readiness.rst scripts/generate_changelog.py --show-diff-on-failure
• DATAFOG_NO_TELEMETRY=1 DO_NOT_TRACK=1 .venv312/bin/python -m sphinx -b html docs docs/_build/html
• DATAFOG_NO_TELEMETRY=1 DO_NOT_TRACK=1 .venv312/bin/python -m pytest tests/test_runtime_dependency_safety.py tests/test_no_network_core.py tests/test_de_pii_regex.py tests/test_regex_annotator.py -q
• 4.5 release-note generator smoke via monkeypatched get_current_version() == "4.5.0"
• git diff --check
• DATAFOG_NO_TELEMETRY=1 DO_NOT_TRACK=1 .venv312/bin/python -m pytest -m "not slow" -q
• DATAFOG_INSTALL_PROFILE=<profile> .venv312/bin/python -m pytest tests/test_install_profiles.py -q for core, cli, nlp, nlp-advanced, ocr, distributed, and web
• DATAFOG_INSTALL_PROFILE=ocr DATAFOG_REQUIRE_TESSERACT=1 .venv312/bin/python -m pytest tests/test_install_profiles.py -q
• .venv312/bin/pyproject-build --wheel && .venv312/bin/python scripts/check_wheel_size.py

Notes

• This is stacked on the current 4.5 sequence through DFPY-68: Validate Python 3.13 optional profiles #147.
• It intentionally keeps the development package version at 4.4.0a5; the final stable path should publish 4.5.0 with version_override=4.5.0 or a dedicated stable-release bump.

Linear: DFPY-79