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

manual_src/templates/includes/sidebar.html

@@ -0,0 +1,22 @@
+{# retoor <retoor@molodetz.nl> #}
+<aside class="sidebar">
+    <div class="sidebar-header">
+        <h1><a href="{{ static_prefix }}index.html">{{ site.name }}</a></h1>
+        <div class="version">v{{ site.version }}</div>
+    </div>
+    {% include 'includes/search_box.html' %}
+    <nav class="sidebar-nav" id="sidebar-nav" aria-label="Main navigation">
+        {% for section in nav.sections %}
+        <div class="section">
+            <span class="section-title">{{ section.title }}</span>
+            <ul>
+                {% for page in section.pages %}
+                {% set page_url = section.directory ~ "/" ~ page.file ~ ".html" %}
+                {% set is_active = current_path == page_url %}
+                <li><a href="{{ static_prefix }}{{ page_url }}"{% if is_active %} class="active"{% endif %}>{{ page.title }}</a></li>
+                {% endfor %}
+            </ul>
+        </div>
+        {% endfor %}
+    </nav>
+</aside>