add project docs and research materials; update arch doc with WSL2 dev setup

- docs/: 6 development documents (PRD, tech selection, architecture, risks, roadmap, design workflow)
- research/: FIRE background materials, personal plan, Excel calculator
- 03-架构设计.md: add Section 8 documenting WSL2 → Windows browser dev environment (Vite host config, access URLs, mobile debugging tip)

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

.gitignore

@@ -1,11 +1,11 @@
-# ---> Vue
-# gitignore template for Vue.js projects
-#
-# Recommended template: Node.gitignore
-
-# TODO: where does this rule come from?
-docs/_book
-
-# TODO: where does this rule come from?
-test/
-
+# ---> Vue
+# gitignore template for Vue.js projects
+#
+# Recommended template: Node.gitignore
+
+# TODO: where does this rule come from?
+docs/_book
+
+# TODO: where does this rule come from?
+test/
+