feat: add buildmanual target, faker demo, subprocess examples, and contributing sidebar to manual

Add Makefile buildmanual target for manual generation and include faker_demo.wren, subprocess_async_demo.wren, subprocess_concurrent_demo.wren, and subprocess_fiber_demo.wren example scripts. Update manual sidebar across api pages to link new web-server tutorial and contributing section with module architecture, pure-wren/c-backed modules, foreign classes, async patterns, testing, and documentation pages.

test/faker/seeding.wren

@@ -0,0 +1,28 @@
+// retoor <retoor@molodetz.nl>
+
+import "faker" for Faker
+
+Faker.seed(12345)
+var name1 = Faker.name()
+var email1 = Faker.email()
+var city1 = Faker.city()
+var int1 = Faker.randomInt(1, 100)
+
+Faker.seed(12345)
+var name2 = Faker.name()
+var email2 = Faker.email()
+var city2 = Faker.city()
+var int2 = Faker.randomInt(1, 100)
+
+System.print(name1 == name2) // expect: true
+System.print(email1 == email2) // expect: true
+System.print(city1 == city2) // expect: true
+System.print(int1 == int2) // expect: true
+
+Faker.seed(99999)
+var name3 = Faker.name()
+System.print(name1 != name3) // expect: true
+
+Faker.reset()
+
+System.print("Seeding tests passed") // expect: Seeding tests passed