docs: add Diátaxis taxonomy labels to documentation categories

- Update sidebars.js with explicit category definitions
- Modify how-to guides category description
- Create reference/explanation category scaffolding
- Align documentation structure with Diátaxis framework

Author: youngjungithub

website/docs/explanation/_category_.json

@@ -0,0 +1,9 @@
+{
+  "label": "Explanation",
+  "documentation_type": "explanation",
+  "position": 5,
+  "link": {
+    "type": "generated-index",
+    "description": "Conceptual guides explaining api-ts architecture and design decisions."
+  }
+}

website/docs/explanation/parsing-codec-chaining.md

@@ -0,0 +1,102 @@
+# Decoding JSON from Headers, Query Parameters, and URL Parameters
+
+Though we know headers, URL parameters, and query parameters will be received as a
+`string` or `string[]` value, due to a limitation in api-ts, `httpRequest` only accepts
+codecs that decode values starting from the `unknown` type. Consequently, decoding a
+header, URL parameter, or query parameter with a codec like `JsonFromString`, which can
+only decode values typed as `string`, will produce a error like:
+
+```
+Type 'Type<Json, string, string>' is not assignable to type 'Mixed'.
+  Types of property 'validate' are incompatible.
+    Type 'Validate<string, Json>' is not assignable to type 'Validate<unknown, any>'.
+      Type 'unknown' is not assignable to type 'string'.
+```
+
+There's a straightforward pattern you can use when you have a value typed as `unknown`
+but need to decode it with a codec that can only decode a narrower type. This pattern is
+called <em>codec chaining</em>:
+
+```typescript
+declare const JsonFromString: t.Type<Json, string, string>;
+declare const t.string: t.Type<string, string, unknown>;
+
+const myCodec: t.Type<Json, string, unknown> = t.string.pipe(JsonFromString);
+```
+
+Here, `t.string` decodes a value from `unknown` to `string`, and then `JsonFromString`
+decodes the same value from `string` to `Json`.
+
+For example:
+
+```typescript
+import * as t from 'io-ts';
+import { nonEmptyArray, JsonFromString, NumberFromString } from 'io-ts-types';
+import { httpRequest, optional } from '@api-ts/io-ts-http';
+
+// Define the Filter type for the JSON string
+const Filter = t.type({
+  category: t.string,
+  tags: t.array(t.string),
+  price: t.type({
+    min: t.number,
+    max: t.number,
+  }),
+});
+
+// Define the SearchRequest codec
+const SearchRequest = httpRequest({
+  params: {
+    userId: NumberFromString,
+  },
+  query: {
+    q: t.string,
+    filter: t.string.pipe(JsonFromString).pipe(Filter),
+    tags: nonEmptyArray(t.string),
+    sort: optional(t.string),
+  },
+  headers: {
+    authorization: t.string,
+  },
+});
+
+// Example request object
+const example = {
+  params: {
+    userId: '84938492',
+  },
+  query: {
+    q: 'test',
+    filter:
+      '{"category":"books","tags":["crypto","trading"],"price":{"min":10,"max":50}}',
+    tags: ['tag1', 'tag2', 'tag3'],
+    sort: 'price',
+  },
+  headers: {
+    authorization: 'Bearer token',
+  },
+};
+
+// Decode the example
+const decoded = SearchRequest.decode(example);
+if (decoded._tag === 'Right') {
+  console.log(decoded);
+  /* 
+    Expected decoded output
+    {
+        userId: 84938492,
+        q: 'test',
+        filter: {
+        category: 'books',
+        tags: ['crypto', 'trading'],
+        price: { min: 10, max: 50 },
+        },
+        tags: ['tag1', 'tag2', 'tag3'],
+        sort: 'price',
+        authorization: 'Bearer token',
+    };
+    */
+} else {
+  console.error('Decoding failed:', decoded.left);
+}
+```

website/docs/how-to-guides/_category_.json

@@ -1,5 +1,6 @@
 {
   "label": "How-To Guides",
+  "documentation_type": "how-to_guide",
   "position": 3,
   "link": {
     "type": "generated-index",

website/docs/reference/_category_.json

@@ -0,0 +1,9 @@
+{
+  "label": "Reference",
+  "documentation_type": "reference",
+  "position": 4,
+  "link": {
+    "type": "generated-index",
+    "description": "Technical reference documentation for api-ts components"
+  }
+}

website/docs/tutorial-basics/_category_.json

@@ -1,5 +1,6 @@
 {
   "label": "Tutorial - Basics",
+  "documentation_type": "tutorial",
   "position": 2,
   "link": {
     "type": "generated-index",