chore: initial project scaffolding

Add project configuration, documentation and development tooling:
- flake.nix dev shell with Go, golangci-lint, turbojpeg
- .envrc sourcing sops-encrypted .secrets.env
- golangci-lint v2 config
- opencode.json MCP + LSP wiring
- AGENTS.md development guidelines

opencode.json

@@ -0,0 +1,37 @@
+{
+  "$schema": "https://opencode.ai/config.json",
+  "references": {
+    "obs-teleport": {
+      "repository": "fzwoch/obs-teleport",
+      "description": "Reference implementation of the Teleport protocol used by the OBS receiver. Consult for packet layouts (JPEG/WAVE headers), multicast discovery (AnnouncePayload), and sender behavior when implementing teleportfling."
+    }
+  },
+  "mcp": {
+    "gitea": {
+      "type": "local",
+      "command": ["gitea-mcp", "-t", "stdio"],
+      "environment": {
+        "GITEA_HOST": "http://homeserver:3050",
+        "GITEA_ACCESS_TOKEN": "{env:GITEA_ACCESS_TOKEN}"
+      }
+    },
+    "obs": {
+      "type": "local",
+      "command": ["npx", "-y", "obs-mcp"],
+      "environment": {
+        "OBS_WEBSOCKET_URL": "ws://localhost:4455",
+        "OBS_WEBSOCKET_PASSWORD": "{env:OBS_WEBSOCKET_PASSWORD}"
+      }
+    }
+  },
+  "lsp": {
+    "gopls": {
+      "command": ["gopls"],
+      "extensions": [".go"]
+    },
+    "nixd": {
+      "command": ["nixd"],
+      "extensions": [".nix"]
+    }
+  }
+}