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/pathlib/absolute.wren

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+// retoor <retoor@molodetz.nl>
+
+import "pathlib" for Path
+
+var p1 = Path.new("/home/user")
+System.print(p1.isAbsolute) // expect: true
+System.print(p1.root) // expect: /
+System.print(p1.anchor) // expect: /
+
+var p2 = Path.new("relative/path")
+System.print(p2.isAbsolute) // expect: false
+System.print(p2.root) // expect:
+System.print(p2.anchor) // expect:

test/pathlib/construction.wren

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+// retoor <retoor@molodetz.nl>
+
+import "pathlib" for Path
+
+var p1 = Path.new("/home/user/file.txt")
+System.print(p1.toString) // expect: /home/user/file.txt
+
+var p2 = Path.new("")
+System.print(p2.toString) // expect:
+
+var p3 = Path.new(p1)
+System.print(p3.toString) // expect: /home/user/file.txt
+
+var p4 = Path.new("/home") / "user" / "file.txt"
+System.print(p4.toString) // expect: /home/user/file.txt

test/pathlib/name_stem_suffix.wren

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+// retoor <retoor@molodetz.nl>
+
+import "pathlib" for Path
+
+var p1 = Path.new("/home/user/file.tar.gz")
+System.print(p1.name) // expect: file.tar.gz
+System.print(p1.stem) // expect: file.tar
+System.print(p1.suffix) // expect: .gz
+System.print(p1.suffixes) // expect: [.tar, .gz]
+
+var p2 = Path.new("/home/user/file.txt")
+System.print(p2.name) // expect: file.txt
+System.print(p2.stem) // expect: file
+System.print(p2.suffix) // expect: .txt
+System.print(p2.suffixes) // expect: [.txt]
+
+var p3 = Path.new("/home/user/noext")
+System.print(p3.name) // expect: noext
+System.print(p3.stem) // expect: noext
+System.print(p3.suffix) // expect:
+System.print(p3.suffixes) // expect: []
+
+var p4 = Path.new("/home/user/.hidden")
+System.print(p4.name) // expect: .hidden
+System.print(p4.stem) // expect: .hidden
+System.print(p4.suffix) // expect:
+System.print(p4.suffixes) // expect: []

test/pathlib/navigation.wren

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+// retoor <retoor@molodetz.nl>
+
+import "pathlib" for Path
+
+var p1 = Path.new("/home/user/file.txt")
+System.print(p1.parent) // expect: /home/user
+System.print(p1.parent.parent) // expect: /home
+System.print(p1.parent.parent.parent) // expect: /
+
+var p2 = Path.new("/home/user/file.txt")
+var parents = p2.parents
+System.print(parents.count) // expect: 3
+System.print(parents[0]) // expect: /home/user
+System.print(parents[1]) // expect: /home
+System.print(parents[2]) // expect: /
+
+var p3 = Path.new("relative/path")
+System.print(p3.parent) // expect: relative
+
+var p4 = Path.new("file.txt")
+System.print(p4.parent) // expect: .

test/pathlib/parts.wren

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+// retoor <retoor@molodetz.nl>
+
+import "pathlib" for Path
+
+var p1 = Path.new("/home/user/file.txt")
+System.print(p1.parts) // expect: [/, home, user, file.txt]
+
+var p2 = Path.new("relative/path/file.txt")
+System.print(p2.parts) // expect: [relative, path, file.txt]
+
+var p3 = Path.new("")
+System.print(p3.parts) // expect: []
+
+var p4 = Path.new("/")
+System.print(p4.parts) // expect: [/]
+
+var p5 = Path.new("file.txt")
+System.print(p5.parts) // expect: [file.txt]