docs: Add SSIS conversion guide with supported components list

[BesikiML]

Summary

Adds comprehensive SSIS to Databricks conversion documentation under a new "Source Systems" section in the Transpile Guide.

Changes

• New documentation structure: Created transpile/source_systems/ folder for source system-specific conversion guides
• Source Systems landing page: Added source_systems/index.mdx with overview and links to available source systems
• SSIS conversion guide: Added source_systems/ssis.mdx with detailed conversion information

What's Included in the SSIS Guide

Each component includes Microsoft name, Spark equivalent, and implementation notes.

Conversion Warnings

• Clear warnings for components with C#/VB.NET code bodies that require manual translation
• Explanations of why certain components are unsupported

Practical Examples

• Derived Column transformations
• Conditional Split patterns
• Lookup transformations with broadcast joins
• Variables and expressions mapping
• ForEach Loop containers
• Script components (Control Flow and Data Flow)
• Package configuration migration (Connection Managers → Databricks secrets)

Complete Conversion Example

• Full end-to-end SSIS package (LoadCustomerData.dtsx) converted to Databricks notebook
• Shows real-world conversion with all components integrated

Implemented

issue: https://github.com/databrickslabs/bladerunner/issues/748

Benefits

• Clear guidance for users converting SSIS packages to Databricks
• Upfront visibility of supported/unsupported components for migration planning
• Scalable structure for adding additional source systems (DataStage, Informatica, etc.)
• Reduces migration risk by highlighting manual conversion requirements

Testing

• Documentation builds successfully
• All internal links resolve correctly
• Sidebar navigation displays properly
• Code examples are properly formatted

Related

• Based on configuration: bb-backend-perl-shared/DefaultConfigs/SSIS/ssis2dws.json
• Complements existing BladeBridge transpiler documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.92%. Comparing base (54c0dfc) to head (c2d3ecf).

Additional details and impacted files

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  Coverage   63.92%   63.92%           
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  Files          99       99           
  Lines        8635     8635           
  Branches      889      889           
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  Hits         5520     5520           
  Misses       2943     2943           
  Partials      172      172           

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[github-actions]

✅ 130/130 passed, 6 flaky, 5 skipped, 10m54s total

Flaky tests:

• 🤪 test_installs_and_runs_local_bladebridge (20.361s)
• 🤪 test_installs_and_runs_pypi_bladebridge (25.797s)
• 🤪 test_transpiles_informatica_to_sparksql (19.711s)
• 🤪 test_transpiles_informatica_to_sparksql_non_interactive[True] (19.932s)
• 🤪 test_transpile_teradata_sql_non_interactive[False] (21.691s)
• 🤪 test_transpile_teradata_sql_non_interactive[True] (5.571s)

_{Running from acceptance #3472}