feat: extend DAB service framework templates

[cshiels-ie]

Summary

• Configure DAB filtering and bounded pagination explicitly.
• Add optional OpenTelemetry support via init --observability.
• Make generated core models auditable and add activity-stream coverage.
• Document the generated DAB integration and remove duplicate development dependencies.

User authentication and OAuth2 are intentionally out of scope because gateway handles authentication and OAuth2 was deferred.

Testing

• uv run ruff check src/platform_service_framework/cli.py tests/test_init.py tests/test_validate.py
• uv run ruff format --check src/platform_service_framework/cli.py tests/test_init.py tests/test_validate.py
• uv run pytest tests/test_completions.py tests/test_source_detection.py -q (13 passed)
• Rendered default and observability Copier projects and compiled generated settings/core/app templates.
• The full init/validate suite requires a clean template checkout; the working tree contains pre-existing untracked .claude/ and CLAUDE.md files, so those tests are left for clean CI execution.

AI Assistance

This change was developed with assistance from OpenCode (openai/gpt-5.6-luna).
All generated code was reviewed, tested, and validated before merging.