test: close coverage gaps and add DB integration test suite

[jravani]

Summary

• Unit tests for previously 0%-covered packages: internal/config, internal/models, internal/api/middleware, internal/api/router, internal/service, plus the remaining untested branches of internal/api/handler and internal/utils (database.go, logger.go).
• New -tags integration suite (testcontainers-go + a real Postgres container) covering the DB-touching paths in internal/utils (ConnectPool), internal/db (TableConstructor.Run()), and internal/db/repository (TabulaRepository queries).
• CI split into unit / integration jobs (mirroring city2tabula's pattern), plus codecov.yml with after_n_builds: 2 so the two uploads land together.
• Removes BuildingRepository/GetByBuildingCode/NewIgnisServiceWithDB (closes BuildingRepository.GetByBuildingCode cannot correctly populate a struct from any table shape #13): while writing repository integration tests, found this path was doubly broken — its unquoted WHERE code_buildingvariant = $1 can't match the quoted mixed-case columns TableConstructor actually creates, and even on a table shaped to match the filter, populateStructFromMap looked values up by the mixed-case JSON tag while Postgres returns unquoted columns lowercased, so fields never populated either way. It was unreachable from any handler (only wired via NewIgnisServiceWithDB, which nothing called), so this is dead-code removal, not a behavior change. The shared struct-mapping helpers it depended on moved to struct_mapper.go, still used by TabulaRepository.GetVariant.

Coverage: config, models, api/middleware, api/router 0% → 100%; utils ~16% → 98.8%; api/handler 62.1% → 97.4%; service 0% → 88.2%; db 0% → 91.8% (integration); db/repository 0% → 89.4% (integration).

Test plan

• go build ./...
• go vet ./... and go vet -tags integration ./...
• go test ./... — all packages pass
• go test -tags integration -timeout 5m ./internal/utils/ ./internal/db/ ./internal/db/repository/ — all pass against a local Docker Postgres

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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