Add project-context.md for spanner-to-sourcedb

[aasthabharill]

b/521739135

[gemini-code-assist]

Summary of Changes

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This pull request introduces documentation and architectural diagrams for the spanner-to-sourcedb reverse replication pipeline. The new context file provides essential information regarding the project's intent, technical stack, logical structure, and best practices, aiming to improve onboarding and maintenance efficiency for developers and automated tools.

Highlights

• Project Documentation: Added a comprehensive project-context.md file to the spanner-to-sourcedb directory to serve as a guide for developers and AI agents.
• Architecture Visualization: Included an architecture diagram in both DOT and SVG formats to provide a clear visual representation of the pipeline's logical components.

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[gemini-code-assist]

Code Review

This pull request adds documentation and architecture diagrams for the Spanner to SourceDb reverse replication pipeline, including a project context markdown file, a Graphviz DOT file, and its corresponding SVG diagram. The review feedback highlights minor typos: 'Metatdata' in the DOT file label (which requires regenerating the SVG) and 'methods.s' in the project context file.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.41%. Comparing base (b8ef535) to head (b36adcd).
⚠️ Report is 31 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3901      +/-   ##
============================================
+ Coverage     55.55%   63.41%   +7.86%     
+ Complexity     7022     2327    -4695     
============================================
  Files          1103      514     -589     
  Lines         67557    29969   -37588     
  Branches       7576     3303    -4273     
============================================
- Hits          37529    19004   -18525     
+ Misses        27612    10004   -17608     
+ Partials       2416      961    -1455     

Components	Coverage Δ
spanner-templates	88.94% <ø> (+0.59%)	⬆️
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	90.16% <ø> (-0.01%)	⬇️
spanner-live-reverse-replication	84.37% <ø> (+0.32%)	⬆️
spanner-bulk-migration	92.58% <ø> (-0.01%)	⬇️
gcs-spanner-dv	90.39% <ø> (+1.44%)	⬆️
see 628 files with indirect coverage changes

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