Implement the following plan:

# Fix Missing `rows.Close()` Memory Leaks in SQLite3 Queries

## Context

Production memory leaks traced to queries that do full table scans (e.g., job state list sorted by `start_time` on all jobs). The root cause is `sql.Rows` objects not being closed after query execution. In Go's `database/sql`, every `rows` returned by `.Query()` holds a database connection and associated buffers until `rows.Close()` is called. Without `defer rows.Close()`, these leak on every code path (both success and error returns).

## Findings

**22 total `.Query()` calls** across the repository layer. **15 have `defer rows.Close()`**. **7 do not** (listed below). Additionally, 1 `Queryx` call in `tags.go` is also missing close.

In `node.go`, `QueryNodes` and `QueryNodesWithMeta` have partial `rows.Close()` only in error paths but **not on the success path** and not via `defer`.

`CountStates` and `CountStatesTimed` in `node.go` also lack `defer rows.Close()` (same partial pattern as above for CountStates, none at all for CountStatesTimed).

## Changes Required

### 1. `internal/repository/stats.go` — 6 functions missing `defer rows.Close()`

Add `defer rows.Close()` immediately after the `if err != nil` check for each:

| Line | Function |
|------|----------|
| 233 | `JobsStatsGrouped` |
| 438 | `JobCountGrouped` |
| 494 | `AddJobCountGrouped` |
| 553 | `AddJobCount` |
| 753 | `jobsStatisticsHistogram` |
| 821 | `jobsDurationStatisticsHistogram` |
| 946 | `jobsMetricStatisticsHistogram` |

Pattern — after each `Query()` error check, add:
```go
rows, err := query.RunWith(r.DB).Query()
if err != nil {
    ...
    return nil, err
}
defer rows.Close()   // <-- ADD THIS
```

### 2. `internal/repository/tags.go` — 2 leaks in `CountTags()`

**Line 282**: `xrows` from `r.DB.Queryx(...)` — add `defer xrows.Close()` after error check.

**Line 333**: `rows` from `q.RunWith(r.stmtCache).Query()` — add `defer rows.Close()` after error check.

### 3. `internal/repository/tags.go` — 3 leaks in `GetTags`, `GetTagsDirect`, `getArchiveTags`

**Line 508** (`GetTags`): add `defer rows.Close()` after error check.
**Line 541** (`GetTagsDirect`): add `defer rows.Close()` after error check.
**Line 579** (`getArchiveTags`): add `defer rows.Close()` after error check.

### 4. `internal/repository/node.go` — 4 functions missing `defer rows.Close()`

**Line 363** (`QueryNodes`): Replace the manual `rows.Close()` in the error path with `defer rows.Close()` immediately after the error check. Remove the explicit `rows.Close()` call on line 375.

**Line 412** (`QueryNodesWithMeta`): Same pattern — add `defer rows.Close()` after error check, remove explicit `rows.Close()` on line 427.

**Line 558** (`CountStates`): Add `defer rows.Close()` after error check. Remove explicit `rows.Close()` on line 569.

**Line 620** (`CountStatesTimed`): Add `defer rows.Close()` after error check. Remove explicit `rows.Close()` on line 633.

## Summary of All Edits

| File | Function | Action |
|------|----------|--------|
| `stats.go:237` | `JobsStatsGrouped` | Add `defer rows.Close()` |
| `stats.go:442` | `JobCountGrouped` | Add `defer rows.Close()` |
| `stats.go:498` | `AddJobCountGrouped` | Add `defer rows.Close()` |
| `stats.go:557` | `AddJobCount` | Add `defer rows.Close()` |
| `stats.go:757` | `jobsStatisticsHistogram` | Add `defer rows.Close()` |
| `stats.go:825` | `jobsDurationStatisticsHistogram` | Add `defer rows.Close()` |
| `stats.go:950` | `jobsMetricStatisticsHistogram` | Add `defer rows.Close()` |
| `tags.go:284` | `CountTags` (xrows) | Add `defer xrows.Close()` |
| `tags.go:336` | `CountTags` (rows) | Add `defer rows.Close()` |
| `tags.go:513` | `GetTags` | Add `defer rows.Close()` |
| `tags.go:546` | `GetTagsDirect` | Add `defer rows.Close()` |
| `tags.go:584` | `getArchiveTags` | Add `defer rows.Close()` |
| `node.go:368` | `QueryNodes` | Add `defer rows.Close()`, remove manual close on L375 |
| `node.go:417` | `QueryNodesWithMeta` | Add `defer rows.Close()`, remove manual close on L427 |
| `node.go:563` | `CountStates` | Add `defer rows.Close()`, remove manual close on L569 |
| `node.go:625` | `CountStatesTimed` | Add `defer rows.Close()`, remove manual close on L633 |

## Verification

1. `go build ./...` — ensure it compiles
2. `go test ./internal/repository/...` — run repository tests
3. `go vet ./internal/repository/...` — static analysis


If you need specific details from before exiting plan mode (like exact code snippets, error messages, or content you generated), read the full transcript at: /Users/jan/.claude/projects/-Users-jan-prg-CC-cc-backend/28147033-ddc8-4056-b064-e0558fbc614e.jsonl

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Check if the fixes are correctly merged in nodes.go