feat(db-tool): hectic-inheritance: bootstrap hectic.created_at / hectic.updated_at inheritance hook

Adds a SQL bundle plus event triggers that enforce `INHERITS (hectic.created_at)`
on every user CREATE TABLE and auto-attach a BEFORE UPDATE row trigger when a
table inherits `hectic.updated_at`. Always-exempt: `hectic`, `information_schema`,
`pg_*`, declarative partitions, temp tables. Per-DB opt-out via the GUC
`hectic.inheritance_extra_excluded_schemas`.

Exposed three ways:
  * `pkgs.hectic.hectic-inheritance` — derivation with the SQL at
    $out/share/hectic/hectic-inheritance.sql
  * `self.lib.hecticInheritance.{sql,path}` — pkgs-free Nix surface
  * `postgres-init` opt-in via `PG_HECTIC_INHERITANCE=1` (HECTIC_INHERITANCE_SQL
    overrides the default)

Test postgres-init-hectic-inheritance covers all six branches: bootstrap,
non-inheriting reject, accepting inheritance, auto updated_at trigger fires,
GUC exclusion, declarative partition exemption.

package/default.nix

@@ -145,6 +145,7 @@ in {
   "db-tool"                    = dbToolPkgs."db-tool";
   "postgres-init"              = dbToolPkgs."postgres-init";
   "postgres-cleanup"           = dbToolPkgs."postgres-cleanup";
+  "hectic-inheritance"         = dbToolPkgs."hectic-inheritance";
   nbt2json                     = pkgs.callPackage ./nbt2json                          {};
   hemar-parser                 = pkgs.callPackage ./hemar/parser                      {};
   AstroTuxLauncher              = pkgs.callPackage ./AstroTuxLauncher.nix             {};