feat: add setup-ai bootstrap

[avezou]

setup-ai.sh:

• build whisper-cli with the current Cmake-based layout
• download models/ggml-medium.bin
• prompt for LLM provider settings and write them to .env
• update docs to reflect changes

Summary

Adds a one-shot setup-ai.sh bootstrap for the AI pipeline so users can setup whisper.cpp, download the default mode, and configure LLM provider from one guided flow.

• clone/recover whisper.cpp and build whisper-cli
• download models/ggml-medium.bin
• prompt for LLM provider settins and write them to .env

Changes

• setup-ai.sh  — (NEW) adds the one-shot AI bootstrap flow to clone/build  whisper.cpp , download the model, and write LLM settings into  .env .
•  server/lib/whisper-transcriber.js  — aligns the server’s auto-build path with the current  whisper.cpp  CMake layout so transcription can build the CLI correctly.
•  tests/test-setup-ai.sh  — adds a smoke test that runs the setup script against a fake toolchain and verifies the expected outputs.
•  run-pre-validation.sh  — includes the new setup script test in the repo’s validation flow and runs shell tests with bash.
•  package.json  — adds an  npm run test:setup-ai  shortcut for the new smoke test.
•  README.md  — updates the AI setup docs to point users at  ./setup-ai.sh  and notes the required  cmake  dependency.
•  QUICKSTART.md  — mentions the optional AI bootstrap step in first-time setup.
•  web/js/main.js  — points capability-gating hints at  ./setup-ai.sh  instead of manual whisper.cpp/LLM steps.
•  .gitignore  — ignores the local  whisper.cpp/  checkout and downloaded model files.
•  CHANGELOG.md  — records the new AI bootstrap script in the unreleased notes.

Test Plan

• Server tests pass (npm test)
• Manual test: start session, verify audio
• Tested in Chrome (chromium on Archlinux)
• Tested in Firefox

Screenshots