docs: update README to reflect Tauri 2 + SolidJS stack

[theoryshaw]

• Replace outdated Electron references with Tauri 2, SolidJS, and Vite
• Add prerequisites table (Node.js ≥20.19, Rust, MSVC Build Tools, CMake)
• Add Windows-specific gotchas: pause Dropbox before building, add Defender exclusion for src-tauri/target/
• Fix dev and build commands (npm run tauri:dev / tauri:build)
• Update project structure to match current codebase layout

[theoryshaw]

Summary

The README was significantly out of date, still describing the app as an Electron project. This PR brings it in line with the current architecture and documents the real local development setup based on hands-on testing on Windows.

What changed

• Framework description — replaced Electron with Tauri 2 + SolidJS + Vite as the actual stack
• Prerequisites table — added explicit version requirements for Node.js (≥ 20.19.0), Rust (stable), MSVC Build Tools 2022, and CMake; these are all hard requirements that will cause build failures if missing
• Dev command — replaced npm start with npm run tauri:dev and explained that the first run takes several minutes due to Rust compilation, with subsequent runs being fast
• Windows gotchas section — documents two real failure modes discovered during setup:
  • Dropbox (and other sync clients) locking .tmp files during Rust compilation, causing os error 32 build failures
  • Windows Defender scanning the target/ directory, also causing file-locking errors; fix is to add src-tauri/target/, cargo.exe, and rustc.exe as exclusions
• Build command — replaced the old per-platform Electron build scripts with npm run tauri:build and noted where the output installer lands
• Project structure — updated to reflect the current file layout including bridge.ts, solid/, i18n/, src-tauri/, and types/; removed references to files that no longer exist (main.js Electron process, preload.js, pdfjs/)
• Technologies — replaced Electron with the full current stack and linked to each project's homepage

Test plan

• Verify prerequisites table matches package.json engine requirements and src-tauri/Cargo.toml
• Confirm npm run tauri:dev and npm run tauri:build commands are correct
• Follow the README on a clean machine to validate setup instructions

[theoryshaw]

@DutchSailor
Obviously this was done with AI, so no clue if it's correct.
But these are all the AI's lesson's learned when i went through setting up a local development env for OPS on Windows.