## Summary

Fixes the vendored PostgreSQL schemainspect traversal for circular
selectable dependencies, matching the issue fixed upstream in
`mmkal/pgkit#469`. `PostgreSQL.load_deps_all()` now stops revisiting
signatures during recursive expansion and removes the root selectable
wherever it reappears in circular walks.

The red repro is intentionally preserved as commit `9d21f30` before the
fix commit, so CI/history can show the original failure.

## Before / After

Before:

```ts
await database.load_deps_all();
// RangeError: Maximum call stack size exceeded
```

After:

```ts
await database.load_deps_all();
first.dependent_on_all; // [second.signature]
second.dependent_on_all; // [first.signature]
```

## Verification

- Red repro commit: `9d21f30` failed locally with `RangeError: Maximum
call stack size exceeded`.
- Green fix: `pnpm --dir packages/pg exec vitest run
test/circular-selectable-deps.test.ts`
- Typecheck: `pnpm --filter @sqlfu/pg typecheck`
- Note: `pnpm --filter @sqlfu/pg test --
circular-selectable-deps.test.ts` also loads DB-backed pg suites in this
repo and fails locally without the test Postgres container.

<!-- package-size:start -->
<details>
<summary>Package size — packed 280.5 kB (no change)</summary>

## Package size

|  | main | this PR | Δ |
| - | - | - | - |
| packed | 280.5 kB | 280.5 kB | 0 |
| unpacked | 1.12 MB | 1.12 MB | 0 |
| files | 226 | 226 | 0 |

### `dist/vendor/*.js` bundles

|  | main | this PR | Δ |
| - | - | - | - |
| `vendor/sha256.js` | 4.3 kB | 4.3 kB | 0 |
| `vendor/sql-formatter/*.js` | 94.5 kB | 94.5 kB | 0 |
| `vendor/sqlfu-sqlite-parser/*.js` | 17.2 kB | 17.2 kB | 0 |
| `vendor/standard-schema/*.js` | 2.8 kB | 2.8 kB | 0 |
| `vendor/typesql/*.js` | 134.8 kB | 134.8 kB | 0 |

_Measured with `npm pack --dry-run --json` on `sqlfu` (0.0.3-7 on main
vs 0.0.3-7 on this PR)._

</details>
<!-- package-size:end -->

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Small, targeted fix in schema-inspection dependency expansion with a
focused regression test; no auth, security, or data-path changes.
> 
> **Overview**
> Fixes **stack overflow** when vendored PostgreSQL schemainspect
expands transitive selectable dependencies that form a cycle (aligned
with upstream `mmkal/pgkit#469`).
> 
> `PostgreSQL.load_deps_all()` now tracks a **visited set** during
recursive `get_related_for_item` walks so signatures are not re-entered,
and **strips the root selectable’s signature** from `dependent_on_all` /
`dependents_all` when it would appear again in a circular path. A
**regression test** builds two mutually dependent views and asserts
stable transitive lists instead of a `RangeError`.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
a9dddad. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->