perf(db): add index on sbom_external_node(sbom_id, external_node_ref)

[mrrajan]

Eliminates sequential scan during external node resolution. Verified: Seq Scan → Index Scan on hosted environment.

Implements TC-4750

Assisted-by: Claude Code

Summary by Sourcery

Enhancements:

• Introduce a migration that adds a composite index on sbom_external_node(sbom_id, external_node_ref) to optimize query performance.

[sourcery-ai]

Reviewer's Guide

Adds a new SeaORM migration to create a composite index on sbom_external_node(sbom_id, external_node_ref) and wires it into the migrator so external node resolution can use an index scan instead of a sequential scan.

File-Level Changes

Change	Details	Files
Introduce a new SeaORM migration that creates/drops a composite index on sbom_external_node over (sbom_id, external_node_ref) and register it in the global migrator.	Register a new migration module m0002200_sbom_external_node_ref_index in the migration library and add it to the Migrator::build_migrations chain as a normal migration. Define the Migration::up implementation to create an if-not-exists index named IdxSbomExternalNodeRef on the SbomExternalNode table over SbomId and ExternalNodeRef using SeaORM’s Index builder. Define the Migration::down implementation to drop the index if it exists, mirroring the up migration. Introduce DeriveIden enums (Indexes and SbomExternalNode) to provide identifier names for the index and table/columns in a type-safe way.	migration/src/lib.rs migration/src/m0002200_sbom_external_node_ref_index.rs

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.39%. Comparing base (5f31950) to head (f3daf1c).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2404      +/-   ##
==========================================
+ Coverage   71.37%   71.39%   +0.01%     
==========================================
  Files         441      442       +1     
  Lines       26747    26896     +149     
  Branches    26747    26896     +149     
==========================================
+ Hits        19092    19202     +110     
- Misses       6541     6565      +24     
- Partials     1114     1129      +15     

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[rh-jfuller]

@mrrajan considering current and ongoing work on 0.4.z (which will push to main) I think this PR can be closed ... do you agree ?