fix(scanner): prevent foreign key constraint errors in album participant insertion (#4373)

* fix: prevent foreign key constraint error in album participants

Prevent foreign key constraint errors when album participants contain
artist IDs that don't exist in the artist table. The updateParticipants
method now filters out non-existent artist IDs before attempting to
insert album_artists relationships.

- Add defensive filtering in updateParticipants() to query existing artist IDs
- Only insert relationships for artist IDs that exist in the artist table
- Add comprehensive regression test for both albums and media files
- Fixes scanner errors when JSON participant data contains stale artist references

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: optimize foreign key handling in album artists insertion

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: improve participants foreign key tests

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: clarify comments in album artists insertion query

Signed-off-by: Deluan <deluan@navidrome.org>

* test: add cleanup to album repository tests

Added individual test cleanup to 4 album repository tests that create temporary
artists and albums. This ensures proper test isolation by removing test data
after each test completes, preventing test interference when running with
shuffle mode. Each test now cleans up its own temporary data from the artist,
library_artist, album, and album_artists tables using direct SQL deletion.

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: refactor participant JSON handling for simpler and improved SQL processing

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: update test command description in Makefile for clarity

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: refactor album repository tests to use albumRepository type directly

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

Makefile

@@ -37,7 +37,7 @@ watch: ##@Development Start Go tests in watch mode (re-run when code changes)
 .PHONY: watch
 
 PKG ?= ./...
-test: ##@Development Run Go tests
+test: ##@Development Run Go tests. Use PKG variable to specify packages to test, e.g. make test PKG=./server
 	go test -tags netgo $(PKG)
 .PHONY: test