docs: comprehensive documentation - README, specs, architecture, API reference, UI/UX flow, dev guide

docs/api-reference.md

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+# ComparAIson — API Reference
+
+## Base URL
+
+```
+Development: http://localhost:3000
+Production:  https://comparaison.tophermayor.com
+```
+
+---
+
+## Authentication
+
+All authenticated endpoints use Better Auth session cookies.
+
+### POST `/api/auth/sign-up`
+Create a new account.
+
+**Request:**
+```json
+{
+  "name": "Alex Johnson",
+  "email": "alex@example.com",
+  "password": "securepassword123"
+}
+```
+
+**Response:** `200 OK` — Sets session cookie, returns user object
+
+### POST `/api/auth/sign-in`
+Sign in to existing account.
+
+**Request:**
+```json
+{
+  "email": "alex@example.com",
+  "password": "securepassword123"
+}
+```
+
+**Response:** `200 OK` — Sets session cookie, redirects to callbackUrl
+
+### POST `/api/auth/sign-out`
+Sign out, clears session.
+
+**Response:** `200 OK` — Redirects to `/`
+
+---
+
+## Comparison Endpoints
+
+### POST `/api/compare`
+Start a new comparison research. Returns a Server-Sent Events stream.
+
+**Authentication:** Required
+
+**Request:**
+```json
+{
+  "query": "for modern web development",
+  "items": ["React", "Vue", "Svelte"],
+  "dimensions": ["Performance", "Developer Experience"]
+}
+```
+
+| Field | Type | Required | Description |
+|---|---|---|---|
+| `query` | string | No | Context/focus for the comparison |
+| `items` | string[] | Yes | Items to compare (2-10) |
+| `dimensions` | string[] | No | Optional dimension hints |
+
+**Response:** `200 OK` — `text/event-stream`
+
+SSE event format:
+```
+event: progress
+data: {"status":"researching","message":"Analyzing comparison request...","itemsCompleted":0,"totalItems":3,"currentStep":"Analyzing comparison request..."}
+
+event: progress
+data: {"status":"researching","message":"Researching React...","itemsCompleted":1,"totalItems":3,"currentStep":"Analyzing React"}
+
+event: progress
+data: {"status":"completed","message":"Research complete!","itemsCompleted":3,"totalItems":3,"currentStep":"Done"}
+
+event: done
+data: {"id":"clx123abc","slug":"react-vs-vue-vs-svelte-clx123","data":{...full comparison data...}}
+```
+
+**Error Response:** `400 Bad Request`
+```json
+{ "error": "At least 2 items are required" }
+```
+
+---
+
+## Page Routes
+
+### `GET /`
+Landing page. Public. Shows hero, example comparisons, features.
+
+### `GET /sign-in`
+Sign in form. Public. Redirects to `/compare` on success.
+
+### `GET /sign-up`
+Sign up form. Public. Redirects to `/compare` on success.
+
+### `GET /compare`
+Comparison creation page. **Protected.** Shows item input form + streaming progress.
+
+### `GET /compare/[slug]`
+Comparison results page. Public (if comparison is public). Shows tabbed visualization layout.
+
+**URL format:** `/compare/react-vs-vue-vs-svelte-clx123a`
+
+### `GET /explore`
+Public comparisons feed. Public. Grid layout with search + category filter.
+
+### `GET /profile`
+User profile page. **Protected.** Shows user info, stats, and saved comparisons.
+
+---
+
+## TypeScript Types
+
+### ComparisonRequest
+```typescript
+interface ComparisonRequest {
+  query: string;
+  items: string[];
+  dimensions?: string[];
+}
+```
+
+### ComparisonResult
+```typescript
+interface ComparisonResult {
+  items: ItemResearch[];
+  dimensions: string[];
+  summary: string;
+  recommendation: string;
+}
+```
+
+### ItemResearch
+```typescript
+interface ItemResearch {
+  name: string;
+  description: string;
+  overallScore: number;
+  dimensions: Record<string, DimensionResult>;
+  pros: string[];
+  cons: string[];
+  sources: { title: string; url: string; snippet: string }[];
+}
+```
+
+### DimensionResult
+```typescript
+interface DimensionResult {
+  score: number;       // 1-10
+  summary: string;
+  details: string;
+  pros: string[];
+  cons: string[];
+}
+```
+
+### ResearchProgress (SSE)
+```typescript
+type ResearchProgress =
+  | { stage: "parsing"; message: string }
+  | { stage: "searching"; item: string; results: number }
+  | { stage: "researching"; item: string; progress: number }
+  | { stage: "synthesizing"; message: string }
+  | { stage: "complete"; result: ComparisonResult }
+  | { stage: "error"; error: string };
+```
+
+### ComparisonData (Frontend)
+```typescript
+interface ComparisonData {
+  id: string;
+  userId: string;
+  title: string;
+  query: string;
+  slug: string;
+  status: "researching" | "completed" | "failed";
+  summary: string;
+  items: {
+    name: string;
+    description: string;
+    overallScore: number;
+    dimensions: Record<string, DimensionResult>;
+    pros: string[];
+    cons: string[];
+  }[];
+  dimensions: string[];
+  tags: string[];
+  isPublic: boolean;
+  viewCount: number;
+  createdAt: string;
+  updatedAt: string;
+}
+```