Fix use-after-free bug in postgres example (14-02.zig)

[Copilot]

The examples (macos-latest) CI job was failing in run exe examples-14-02 with ERROR: invalid input syntax for type integer: "" because color_id held a dangling pointer into a freed PGresult buffer.

Root cause

color_id was extracted via std.mem.span(c.PQgetvalue(res, 0, 0)) inside a blk: block that also had defer c.PQclear(res). The defer fires when the block exits — including on break :blk — so by the time color_id was used in the inner loop, the PGresult buffer it pointed into was already freed. On macOS, freed memory is zeroed, so color_id read as "", and PostgreSQL rejected it as an invalid integer.

Fix

Remove the blk: scope. Execute PQexecPrepared for insert_cat_colors directly in the outer inline for body and defer PQclear(color_res) there, so color_id stays valid for the full duration of the inner loop.

// Before: PQclear fires at break :blk, before color_id is used
const color_id = blk: {
    const res = c.PQexecPrepared(...);
    defer c.PQclear(res);           // ← fires here, freeing res's buffer
    ...
    break :blk std.mem.span(c.PQgetvalue(res, 0, 0));
};
// color_id is now a dangling pointer

// After: PQclear deferred to outer loop scope
const color_res = c.PQexecPrepared(...);
defer c.PQclear(color_res);         // ← fires at end of inline for iteration
const color_id = std.mem.span(c.PQgetvalue(color_res, 0, 0));
// color_id remains valid through the inner loop