Add IP-to-country geolocation service

Introduce a geoloc package that stores CIDR-to-country mappings in
PostgreSQL using the native cidr type with a GiST index for fast
containment lookups. Data comes from the ipverse/country-ip-blocks
dataset added as a git submodule.

A standalone geoloc-import command reads the TXT files from disk
and bulk-loads them via COPY. probod wires the service and logs a
warning when the table is empty.

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/coredata/migrations/20260506T084741Z.sql

@@ -0,0 +1,21 @@
+-- Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted, provided that the above
+-- copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+-- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+-- AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+-- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+-- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+-- OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+CREATE TABLE common_ip_country_blocks (
+    cidr         CIDR    NOT NULL,
+    country_code CHAR(2) NOT NULL
+);
+
+CREATE INDEX idx_common_ip_country_blocks_cidr
+    ON common_ip_country_blocks USING gist (cidr inet_ops);