feat(tools): create_project_from_template

Generates a new repo from mathias/template-go-web via Gitea's generate
API, then substitutes __PROJECT_NAME__ and __MODULE_PATH__ placeholders
in six known files (best-effort, partial failure surfaced in result).

Validates name regex, allowlist, template flag, and destination
non-existence before generating. Adds Template field to gitea.Repo.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/gitea/repos.go

@@ -15,6 +15,7 @@ type Repo struct {
 	Private       bool   `json:"private"`
 	CloneURL      string `json:"clone_url"`
 	HTMLURL       string `json:"html_url"`
+	Template      bool   `json:"template"`
 }
 
 func (c *Client) ListRepos(ctx context.Context, owner string, page, limit int) ([]Repo, error) {