fix(spurctld): delete sacctmgr users atomically

[hnotshe]

Fixes #435.

sacctmgr delete user could report Done. without deleting anything because the all-accounts form sent an empty account while the database required an exact account match. The RPC also ignored zero affected rows.

This change deletes matching users and associations rows in one transaction, treats an omitted account as all accounts, and returns NotFound when no row was removed instead of reporting false success.

Testing:

• focused PostgreSQL regression covering one-account deletion, all-account deletion, association cleanup, and repeated deletion
• cargo fmt --all --check
• cargo clippy --workspace --exclude spur-ffi --all-targets --locked
• cargo test --locked

[yansun1996]

The core fix looks correct: a single transaction with proper rollback on partial failure (? drops the tx before commit), ($2 = '' OR account = $2) correctly meaning all-accounts, the summed rows_affected() mapping zero → NotFound, and the test asserting row absence rather than just return codes. A couple of the notes inline are pre-existing rather than introduced here — flagged just for context.

One additional note: the new regression test is #[ignore]'d (it needs DATABASE_URL), so cargo test --locked won't run it in CI. That's consistent with the other DB tests, but it does mean the guard for this fix isn't exercised by default CI.

[Copilot]

Pull request overview

This PR fixes a correctness gap in the accounting RPC for sacctmgr delete user by making user/association deletion transactional, supporting “all accounts” deletion when the account field is omitted, and returning a gRPC NotFound instead of reporting success when nothing was actually deleted.

Changes:

• Update the remove_user gRPC handler to detect zero deletions and return Status::not_found instead of false success.
• Rework db::remove_user to delete matching associations and users rows within a single SQL transaction, treating an empty account as “all accounts”.
• Add a focused PostgreSQL regression test covering one-account deletion, all-account deletion, association cleanup, and repeated deletion behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/spurctld/src/accounting/grpc.rs	Returns NotFound when remove_user deletes zero rows, avoiding misleading “Done.” on no-op deletes.
crates/spurctld/src/accounting/db.rs	Makes remove_user transactional across associations + users, supports empty-account-as-all, and adds a regression test.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 100 lines in your changes missing coverage. Please review.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #451      +/-   ##
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- Coverage   74.25%   74.24%   -0.01%     
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  Files         165      165              
  Lines       59071    59425     +354     
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+ Hits        43862    44116     +254     
- Misses      15209    15309     +100     

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