feat: rename to gitea-mcp-extended and add package publishing workflows

Rename the fork from gitea-mcp to gitea-mcp-extended to reflect the
significantly expanded tool coverage (299 vs upstream's 93 tools).

- Rename Go module path and all import references
- Rename binary to gitea-mcp-extended in Makefile, Dockerfile, .gitignore
- Point .goreleaser.yaml gitea_urls to git.lethalbits.com
- Replace release-tag workflow with goreleaser + Generic Package Registry publishing
- Replace release-nightly workflow with cross-platform build + nightly package publishing
- Update CLAUDE.md project description and tool count

Makefile

@@ -1,5 +1,5 @@
 GO ?= go
-EXECUTABLE := gitea-mcp
+EXECUTABLE := gitea-mcp-extended
 VERSION ?= $(shell git describe --tags --always | sed 's/-/+/' | sed 's/^v//')
 LDFLAGS := -X "main.Version=$(VERSION)"
 
@@ -47,7 +47,7 @@ air: ## Install air for hot reload.
 
 .PHONY: dev
 dev: air ## run the application with hot reload
-	air --build.cmd "make build" --build.bin ./gitea-mcp
+	air --build.cmd "make build" --build.bin ./gitea-mcp-extended
 
 .PHONY: lint
 lint: lint-go ## lint everything