chore: initialize repository with project docs and tooling

- Add persistent docs: PRD, functional design, architecture, repository structure, development guidelines, milestones

- Add brainstorming notes (docs/ideas/)

- Configure tooling: package.json, tsconfig, eslint, prettier, vitest

- Add opencode configuration (commands, skills, agents)

- Add .gitignore for node_modules, .env, data/, backups/, build outputs

.devcontainer/devcontainer.json

@@ -0,0 +1,11 @@
+{
+  "name": "opencode-spec-driven-boilerplate",
+  "image": "mcr.microsoft.com/devcontainers/base:bookworm",
+  "workspaceFolder": "/workspaces/opencode-spec-driven-boilerplate",
+  "features": {
+    "ghcr.io/devcontainers/features/node:1": {
+      "version": "lts"
+    }
+  },
+  "postCreateCommand": "npm install && curl -fsSL https://opencode.ai/install | bash && ln -sf $HOME/.opencode/bin/opencode /usr/local/bin/opencode"
+}