chore: add scripts to build, run and debug

[eguguchkin]

Self-contained dev environment for locally debugging the two‑process (seq‑db store + proxy) without Docker, driven by make targets and supporting VS Code attach with distinguishable process names (seq‑db‑store/seq‑db‑proxy).

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• I have read and followed all requirements in CONTRIBUTING.md;
• I used LLM/AI assistance to make this pull request;

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.48%. Comparing base (8e1fa62) to head (0c3ff38).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #505      +/-   ##
==========================================
+ Coverage   71.43%   71.48%   +0.05%     
==========================================
  Files         239      239              
  Lines       20015    20145     +130     
==========================================
+ Hits        14297    14401     +104     
- Misses       4640     4659      +19     
- Partials     1078     1085       +7     

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