refactor(templates): move the templates out of the gitea subdirectory

The `templates/gitea` subdirectory did not group anything meaningful, since every template of this chart belongs to
Gitea. It only duplicated the chart name in every path and forced the unit tests to spell out
`templates/gitea/<name>.yaml`, while `_helpers.tpl` and `NOTES.txt` already lived directly in `templates`.

All templates now live in `templates`, which matches the layout of the bundled sub-charts and the Helm defaults.

The checksum helper in `templates/_secrets.tpl` built its include path from `$root.Template.BasePath` and therefore
carried the subdirectory in a `printf` format string instead of a literal path. Without adjusting it the chart failed to
render with "no template gitea/templates/gitea/secret_config.yaml associated with template gotpl".

Co-authored-by: Copilot <copilot@github.com>

unittests/helm/config/server-section_domain.yaml

@@ -4,7 +4,7 @@ release:
   namespace: testing
 tests:
   - it: "[default values] uses ingress host for DOMAIN|SSH_DOMAIN|ROOT_URL"
-    template: templates/gitea/secret_inlineConfig.yaml
+    template: templates/secret_inlineConfig.yaml
     asserts:
       - documentIndex: 0
         matchRegex:
@@ -22,7 +22,7 @@ tests:
   ################################################
 
   - it: "[no ingress hosts] uses gitea http service for DOMAIN|SSH_DOMAIN|ROOT_URL"
-    template: templates/gitea/secret_inlineConfig.yaml
+    template: templates/secret_inlineConfig.yaml
     set:
       ingress:
         hosts: []
@@ -43,7 +43,7 @@ tests:
   ################################################
 
   - it: "[provided via values] uses that for DOMAIN|SSH_DOMAIN|ROOT_URL"
-    template: templates/gitea/secret_inlineConfig.yaml
+    template: templates/secret_inlineConfig.yaml
     set:
       gitea.config.server.DOMAIN: provided.example.com
       ingress:
@@ -69,7 +69,7 @@ tests:
   ################################################
 
   - it: "[route enabled] uses route host for DOMAIN|SSH_DOMAIN|ROOT_URL"
-    template: templates/gitea/secret_inlineConfig.yaml
+    template: templates/secret_inlineConfig.yaml
     set:
       route:
         enabled: true
@@ -91,7 +91,7 @@ tests:
   ################################################
 
   - it: "[route tls termination] uses https for ROOT_URL"
-    template: templates/gitea/secret_inlineConfig.yaml
+    template: templates/secret_inlineConfig.yaml
     set:
       route:
         enabled: true
@@ -107,7 +107,7 @@ tests:
   ################################################
 
   - it: "[HTTPRoute enabled] uses first hostname for DOMAIN|SSH_DOMAIN|ROOT_URL"
-    template: templates/gitea/secret_inlineConfig.yaml
+    template: templates/secret_inlineConfig.yaml
     set:
       ingress:
         hosts: []
@@ -137,7 +137,7 @@ tests:
   ################################################
 
   - it: "[HTTPRoute tls] switches ROOT_URL to https"
-    template: templates/gitea/secret_inlineConfig.yaml
+    template: templates/secret_inlineConfig.yaml
     set:
       ingress:
         hosts: []