feat: add merge_all_wren utility, strutil demo, and 7 new API manual pages

Add WrenFileReader class in apps/merge_all_wren.wren for recursive .wren file discovery and content printing. Introduce example/strutil_demo.wren demonstrating case conversion, hex encoding, SHA256 hashing, string repetition, padding, HTML/JSON escaping, and URL encoding/decoding. Create manual/api pages for argparse, dataset, html, markdown, uuid, wdantic, and web modules. Update manual/api/index.html sidebar and module count from 21 to 28, adding links and cards for the new modules.

test/web/response_advanced.wren

@@ -0,0 +1,39 @@
+// retoor <retoor@molodetz.nl>
+
+import "web" for Response
+
+var r1 = Response.redirect("/dashboard", 301)
+System.print(r1.status) // expect: 301
+System.print(r1.headers["Location"]) // expect: /dashboard
+
+var r2 = Response.new()
+r2.status = 404
+r2.body = "Not Found"
+System.print(r2.status) // expect: 404
+System.print(r2.body) // expect: Not Found
+
+var r3 = Response.new()
+r3.header("X-Custom", "value1")
+r3.header("X-Another", "value2")
+System.print(r3.headers["X-Custom"]) // expect: value1
+System.print(r3.headers["X-Another"]) // expect: value2
+
+var r4 = Response.new()
+r4.cookie("session", "abc123")
+r4.body = "test"
+var built = r4.build()
+System.print(built.contains("Set-Cookie: session=abc123")) // expect: true
+
+var r5 = Response.new()
+r5.cookie("auth", "token", {"path": "/", "httpOnly": true, "maxAge": 3600})
+r5.body = "test"
+var built2 = r5.build()
+System.print(built2.contains("Path=/")) // expect: true
+System.print(built2.contains("HttpOnly")) // expect: true
+System.print(built2.contains("Max-Age=3600")) // expect: true
+
+var r6 = Response.text("Hello World")
+var httpResponse = r6.build()
+System.print(httpResponse.contains("HTTP/1.1 200 OK")) // expect: true
+System.print(httpResponse.contains("Content-Length:")) // expect: true
+System.print(httpResponse.contains("Hello World")) // expect: true