Add README and fix CI/CD pipeline for release builds

- README with features, config docs, build instructions, project structure
- Pipeline: add Docker CLI install step, fix DinD volume pattern,
  fix token generation flags (--user git -u calic --raw), proper
  token cleanup by name instead of fragile ID grep
- .gitignore: add dist/ and *.zip

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

README.md

@@ -0,0 +1,97 @@
+# Welcome Screen — Vintage Story Mod
+
+Server-side configurable welcome dialog that opens automatically when players join. Displays Markdown content rendered as VTML (Vintage Text Markup Language) in a scrollable GUI window.
+
+## Features
+
+- **Auto-open on join** — dialog appears when a player connects
+- **Markdown content** — write `welcome.md` in the server data directory, rendered as rich text (headings, bold, italic, links, lists, blockquotes, code)
+- **Mod checker** — server compares client's installed mods against a recommended/blacklisted list and shows the result in the dialog
+- **Reopen with HOME** — players can press HOME to reopen the dialog at any time
+
+## Installation
+
+Download the latest `welcomescreen_x.x.x.zip` from [Releases](../../releases) and place it in your server's `Mods/` directory. Do **not** extract the ZIP.
+
+This is a **universal** mod — it must be installed on both server and client.
+
+## Configuration
+
+All config files are auto-generated on first run in the server's `ModConfig/` directory.
+
+### `WelcomeScreenConfig.json`
+
+```json
+{
+  "Title": "Welcome",
+  "WelcomeFile": "welcome.md"
+}
+```
+
+- `Title` — dialog window title
+- `WelcomeFile` — path to the Markdown file (relative to server data dir)
+
+### `WelcomeScreenModCheck.json`
+
+```json
+{
+  "Enabled": true,
+  "RecommendedMods": [
+    { "ModId": "rpvoicechat", "DisplayName": "RPVoiceChat", "Reason": "Proximity voice chat" }
+  ],
+  "BlacklistedMods": []
+}
+```
+
+- `RecommendedMods` — mods the server suggests clients should have
+- `BlacklistedMods` — mods the server disallows (shown as warning)
+
+### `welcome.md`
+
+Place this file in the server's data directory. Standard Markdown syntax is supported:
+
+```markdown
+# Server Name
+
+Welcome to our server!
+
+## Rules
+1. Be respectful
+2. No griefing
+
+**Have fun!**
+```
+
+## Building
+
+Requires .NET 8 SDK and the Vintage Story API DLLs in `lib/`.
+
+```bash
+# Build locally
+./build.sh
+
+# Build and install to server
+./build.sh --install
+```
+
+## Project Structure
+
+```
+src/
+  WelcomeScreenMod.cs      Main mod — server/client logic, network packets, config
+  WelcomeScreenDialog.cs    GUI dialog with scrollable VTML content
+  MarkdownToVtml.cs         Markdown → VTML converter
+resources/
+  modinfo.json              Mod metadata (version, dependencies)
+lib/
+  VintagestoryAPI.dll       VS API reference (not distributed)
+  protobuf-net.dll          Protobuf serialization (not distributed)
+```
+
+## CI/CD
+
+Push a tag (`v*`) to trigger the build pipeline, which compiles the mod, packages the ZIP, and creates a Gitea release with the artifact attached.
+
+## License
+
+Private mod — not publicly distributed.