Add UUID-based template IDs and team-scoped template directory layout

Introduces internal/layout package for centralized path construction,
migrates templates from name-based TEXT primary keys to UUID PKs with
team-scoped directories (WRENN_DIR/images/teams/{team_id}/{template_id}).
The built-in minimal template uses sentinel zero UUIDs. Proto messages
carry team_id + template_id alongside deprecated template name field.
Team deletion now cleans up template files across all hosts.

db/queries/templates.sql

@@ -1,15 +1,23 @@
 -- name: InsertTemplate :one
-INSERT INTO templates (name, type, vcpus, memory_mb, size_bytes, team_id)
-VALUES ($1, $2, $3, $4, $5, $6)
+INSERT INTO templates (id, name, type, vcpus, memory_mb, size_bytes, team_id)
+VALUES ($1, $2, $3, $4, $5, $6, $7)
 RETURNING *;
 
 -- name: GetTemplate :one
-SELECT * FROM templates WHERE name = $1;
+SELECT * FROM templates WHERE id = $1;
 
 -- name: GetTemplateByTeam :one
 -- Platform templates (team_id = 00000000-...) are visible to all teams.
 SELECT * FROM templates WHERE name = $1 AND (team_id = $2 OR team_id = '00000000-0000-0000-0000-000000000000');
 
+-- name: GetTemplateByName :one
+-- Look up a template by team_id and name (exact team match, no global fallback).
+SELECT * FROM templates WHERE team_id = $1 AND name = $2;
+
+-- name: GetPlatformTemplateByName :one
+-- Check if a global (platform) template exists with the given name.
+SELECT * FROM templates WHERE team_id = '00000000-0000-0000-0000-000000000000' AND name = $1;
+
 -- name: ListTemplates :many
 SELECT * FROM templates ORDER BY created_at DESC;
 
@@ -25,7 +33,15 @@ SELECT * FROM templates WHERE (team_id = $1 OR team_id = '00000000-0000-0000-000
 SELECT * FROM templates WHERE (team_id = $1 OR team_id = '00000000-0000-0000-0000-000000000000') AND type = $2 ORDER BY created_at DESC;
 
 -- name: DeleteTemplate :exec
-DELETE FROM templates WHERE name = $1;
+DELETE FROM templates WHERE id = $1;
 
 -- name: DeleteTemplateByTeam :exec
 DELETE FROM templates WHERE name = $1 AND team_id = $2;
+
+-- name: DeleteTemplatesByTeam :exec
+-- Bulk delete all templates owned by a team (for team soft-delete cleanup).
+DELETE FROM templates WHERE team_id = $1;
+
+-- name: ListTemplatesByTeamOnly :many
+-- List templates owned by a specific team (NOT including platform templates).
+SELECT * FROM templates WHERE team_id = $1 ORDER BY created_at DESC;