feat: expand .gitignore templates for remaining project types

[tbitcs]

Summary

The .gitignore template covers ~12 types but several are missing or incomplete.

Missing / Incomplete Coverage

• data-ml: .ipynb_checkpoints/, mlruns/, wandb/, data/raw/ (large files)
• microservices: docker volumes, .env files, service-specific build dirs
• monorepo: .turbo/, .nx/, per-package build outputs
• api-specification: generated/ directory, node_modules for spectral
• browser-extension: web-ext-artifacts/, .crx, .xpi
• spec-document / user-manual: _site/, site/, .cache/ (MkDocs/Sphinx build dirs)
• business-plan / legal-compliance: ~$*.docx (Office lock files), .tmp
• patent-application: correspondence drafts, office action responses
• requirements-mgmt: baselines/archive/, generated reports
• mobile-app: expand with Flutter (.dart_tool/), React Native (ios/Pods/)
• dotnet-app: add .vs/, packages/, NuGet caches

Implementation

Add conditional blocks to gitignore.j2 for each missing type.

[tbitcs]

Implemented in a8db64c