Add .editorconfig, broaden .gitignore, drop dead Drone refs (closes #72)

Add the canonical .editorconfig from sneak/prompts verbatim. Broaden .gitignore to cover secrets (.env, .env.*, *.key, *.pem), OS files, editor files, and Go artifacts while keeping every repo-specific entry; no tracked file becomes ignored, and bin/gitrev.sh stays tracked despite the /bin/ rule. Remove the stale .drone.yml ignore entry and the DRONE_COMMIT_SHA branch from bin/gitrev.sh, left from the Gitea Actions migration; the GITREV and git-describe paths still work.

A reader may trip over .editorconfig saying four spaces for every file while Go files are tab-indented: gofmt governs Go, editorconfig does not, and the file is taken verbatim by policy.

Disclosure: the worker's cold docker build hit the 10s test timeout in the gpg signature test; this change has no Go code, and that timeout is tracked by issues 67 and 62.

Model: opus-4-8 (implementation); fable-5-1 (merge)

.gitignore

@@ -10,5 +10,24 @@ modcache.tzst
 # Generated manifest files
 .index.mf
 
-# Stale files
-.drone.yml
+# Secrets
+.env
+.env.*
+*.key
+*.pem
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Editor files
+*.swp
+*.swo
+*~
+.idea/
+.vscode/
+
+# Go build artifacts
+*.log
+*.out
+*.test