feat: add wasm build targets, profile hooks, os_demo example, and restructure manual source

- Add `wasm`, `wasm-clean`, and `install-emscripten` phony targets to Makefile for WebAssembly cross-compilation
- Insert `WREN_PROFILE_ENTER`/`WREN_PROFILE_EXIT` macros in `wren_vm.h` and `wren_vm.c` to support optional runtime profiling via `WREN_PROFILE_ENABLED`
- Create `example/os_demo.wren` demonstrating Platform, Process, and conditional exit usage
- Update `example/regex_demo.wren` to import `Match` and exercise Match object properties, groups, and `matchAll`
- Remove static HTML manual pages (`base64.html`, `dns.html`, `json.html`) and replace with structured `manual_src/` directory containing Jinja2 templates, YAML metadata, and content pages
- Expand `README.md` with build targets table, manual building instructions, source layout, and guide for adding new module documentation

example/regex_demo.wren

@@ -1,6 +1,6 @@
 // retoor <retoor@molodetz.nl>
 
-import "regex" for Regex
+import "regex" for Regex, Match
 
 System.print("=== Regex Module Demo ===\n")
 
@@ -128,3 +128,35 @@ var sentence = "hello, world; foo bar"
 var tokens = tokenSeparator.split(sentence)
 System.print("Input: %(sentence)")
 System.print("Tokens: %(tokens)")
+
+System.print("\n--- Match Object ---")
+var emailRe = Regex.new("(\\w+)@(\\w+)\\.(\\w+)")
+var match = emailRe.match("Contact: alice@example.com for info")
+if (match != null) {
+    System.print("Full match: %(match.text)")
+    System.print("Start index: %(match.start)")
+    System.print("End index: %(match.end)")
+    System.print("group(0): %(match.group(0))")
+    System.print("group(1): %(match.group(1))")
+    System.print("group(2): %(match.group(2))")
+    System.print("group(3): %(match.group(3))")
+}
+
+System.print("\n--- Groups Property ---")
+var dateRe = Regex.new("(\\d{4})-(\\d{2})-(\\d{2})")
+var dateMatch = dateRe.match("Date: 2024-01-15")
+if (dateMatch != null) {
+    System.print("groups[0] (full match): %(dateMatch.groups[0])")
+    System.print("groups[1] (year): %(dateMatch.groups[1])")
+    System.print("groups[2] (month): %(dateMatch.groups[2])")
+    System.print("groups[3] (day): %(dateMatch.groups[3])")
+    System.print("Total groups: %(dateMatch.groups.count)")
+}
+
+System.print("\n--- Find All Matches ---")
+var numRe = Regex.new("\\d+")
+var allMatches = numRe.matchAll("Order 123 has 5 items at $99 each")
+System.print("Found %(allMatches.count) numbers:")
+for (m in allMatches) {
+    System.print("  '%(m.text)' at position %(m.start)-%(m.end)")
+}