Improve README: tech stack, resources, collapsible issues, credential tables, contributors

[compwron]

Summary

• Tech Stack table — Ruby/Rails/Postgres/Node versions and key libraries (Hotwire, Stimulus, RSpec, StandardRB) surfaced near the top
• Resources section — links to ADRs, DB diagram, product sense, wiki, and calendar moved up from the bottom so they're easy to find
• Codespaces: remove EXPERIMENTAL label — the setup has been stable; the label discouraged contributors unnecessarily; step 4 now cross-links to the credentials table
• Common issues → collapsible <details> blocks — six issues are now individually expandable so the list doesn't overwhelm first-time readers
• Seed credentials → tables — passwords are now inline next to each email, and local + QA URLs are shown side-by-side
• QA environment subsection — casa-qa.herokuapp.com was buried in a parenthetical; it now has its own named section
• Proper ### subheadings inside Running the App — "Local email", "Running Tests", and "Cleaning up" were bold text, not real headings; fixed so they appear in the TOC
• Frontend Architecture subsection — the orphaned "Stimulus" paragraph is expanded into a proper section explaining Hotwire/Turbo/Stimulus with a pointer to the controllers directory
• Keeping Your Local Environment Up to Date — bin/update and After Party tasks moved into a dedicated section so developers know to run this after every git pull main
• Contributors section — all-contributors spec and bot instructions added so contributors can request attribution
• Windows platform entry — "Help Wanted" removed; now links to the WSL guide as the recommended Windows path
• TOC updated to reflect all new sections (re-run npx doctoc README.md to finalize the generated anchors)

Test plan

• Read through the rendered README on GitHub and verify all links resolve
• Confirm <details> blocks expand/collapse correctly in the GitHub Markdown renderer
• Re-run npx doctoc README.md and commit the result if anchor hashes differ from the manually updated TOC
• Verify QA environment URL is still live at https://casa-qa.herokuapp.com/

🤖 Generated with Claude Code