feat: Add interview pipeline, TTS, and transcription endpoints

[mlarsen-source]

Summary

Implements the core interview pipeline: POST /speech/tts streams Groq Orpheus audio for the interviewer voice, and POST /speech/transcribe sends audio to Groq Whisper for segment-level transcription then scores each segment with the local wav2vec2 emotion model. Introduces InterviewClient, a full-session interview UI that replaces the home page placeholder, with interviewer persona selection, voice activity detection, automatic recording flow, and per-segment arousal/dominance/valence display. Moves AGENTS.md and CLAUDE.md from frontend/ to the repository root, expands them to project-wide scope, and adds docs/architecture.md with a full system data-flow diagram. Updates all setup documentation and agent workflows to reflect Groq as the speech provider and the one-time Orpheus terms-acceptance requirement.

What's new

Surface	Status	Layer
POST /speech/tts	new	Backend
POST /speech/transcribe	new (was empty TODO)	Backend
Interview UI (/)	new	Frontend
/dev/transcribe debug page	new	Frontend
Question bank + interviewer personas	new	Frontend data
AGENTS.md / CLAUDE.md	moved from frontend/ to root, expanded	Config
docs/architecture.md	new	Documentation
docs/agent-workflows/run-project.md	new	Documentation

File-by-file changes

Backend — API

• backend/app.py: Added OPTIONS to allow_methods in CORS middleware so multipart file-upload preflight requests from the browser are not blocked.
• backend/requirements.txt: Added groq>=0.9.0 as the Groq SDK dependency; updated the speech-to-text comment to reflect Groq Whisper replacing OpenAI.
• backend/services/speech_to_text/router.py: Replaced the empty TODO stub with full implementations of POST /speech/tts (Groq Orpheus → WAV) and POST /speech/transcribe (Groq Whisper segmentation + per-segment wav2vec2 scoring); uses os.environ.get for the API key and raises HTTP 503 at request time when the key is absent so a missing key does not crash backend startup.

Frontend — Interview UI

• frontend/app/InterviewClient.tsx: New client component implementing the full interview state machine — idle, playing (TTS), recording (MediaRecorder + Web Audio VAD), processing, and done — with interviewer selection, abort-signal-gated fetch calls to /speech/tts and /speech/transcribe, and per-session used-question tracking via a caller-owned Set ref.
• frontend/app/InterviewClient.module.css: New module stylesheet for InterviewClient; all color values reference semantic tokens defined in globals.css.
• frontend/app/page.tsx: Replaced the static placeholder home page with InterviewClient so the root route is the live interview UI.

Frontend — Dev page

• frontend/app/dev/transcribe/page.tsx: New route entry point for the transcription debug page at /dev/transcribe.
• frontend/app/dev/transcribe/TranscribeDevClient.tsx: New dev-only client component that records audio in accumulated WebM chunks and sends each to POST /speech/transcribe, displaying sent-chunk status and returned segments side by side in real time.
• frontend/app/dev/transcribe/TranscribeDevClient.module.css: New module stylesheet for the dev transcribe page; all color values reference semantic tokens.

Frontend — Styles

• frontend/app/globals.css: Added 18 semantic color tokens (--color-surface, --color-danger, --color-muted, etc.) so component module files reference tokens rather than hard-coded hex values.

Frontend — Data

• frontend/lib/prompts/interviewers.ts: New module defining the six Groq Orpheus interviewer personas (name, title, voice name) and the default selection.
• frontend/lib/prompts/questions.ts: New module with a 20-question bank (1 intro, 10 technical, 10 behavioral) and pickRandomQuestion(usedIds) that accepts a caller-owned Set to avoid module-level mutable state.

Agent configuration

• frontend/AGENTS.md: Deleted — file moved to repository root and expanded to project-wide scope.
• frontend/CLAUDE.md: Deleted — file moved to repository root.
• AGENTS.md: New at repository root; expanded from frontend-only conventions to project-wide scope covering pipeline architecture, backend endpoints, Groq Orpheus setup requirement, run-project trigger phrases, and environment variable table.
• CLAUDE.md: New at repository root; thin pointer to AGENTS.md, replacing the deleted frontend/CLAUDE.md.

Documentation

• README.md: Updated setup steps (added numbered Groq Orpheus terms-acceptance step with symptom description), updated repo structure tree, and updated stack table to reflect Groq Whisper and Orpheus as the speech provider.
• backend/.env.example: Added GROQ_API_KEY entry with console URL; reorganized comments to reflect Groq as the primary speech dependency.
• backend/README.md: Added POST /speech/tts endpoint entry and full request/response documentation; updated POST /speech/transcribe status to done with curl example; added score-interpretation table.
• docs/architecture.md: New document with full system diagram, step-by-step pipeline walkthrough for all seven stages, data schemas, key design decisions, environment variable table, and local dev URLs.
• docs/agent-workflows/README.md: Updated references from frontend/AGENTS.md to AGENTS.md; added run-project.md to the workflow table.
• docs/agent-workflows/code-quality-review.md: Updated frontend/AGENTS.md references to AGENTS.md.
• docs/agent-workflows/css-and-component-standards-review.md: Updated frontend/AGENTS.md references to AGENTS.md.
• docs/agent-workflows/feature-implementation-planning.md: Updated frontend/AGENTS.md references to AGENTS.md.
• docs/agent-workflows/figma-design-to-code.md: Updated frontend/AGENTS.md references to AGENTS.md.
• docs/agent-workflows/pre-merge-full-review.md: Updated frontend/AGENTS.md references to AGENTS.md.
• docs/agent-workflows/run-project.md: New workflow document for agent-driven project startup; covers state assessment, prerequisite fixes, Groq Orpheus terms check, sequential backend/frontend launch, stop instructions, and error reference table.
• docs/agent-workflows/test-suite-quality-review.md: Updated frontend/AGENTS.md references to AGENTS.md.

Environment variables

• GROQ_API_KEY — add