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/breadcrumb.html

@@ -0,0 +1,12 @@
+{# retoor <retoor@molodetz.nl> #}
+<nav class="breadcrumb">
+    <a href="{{ static_prefix }}index.html">Home</a>
+    {% for crumb in breadcrumb %}
+    <span class="separator">/</span>
+    {% if loop.last %}
+    <span>{{ crumb.title }}</span>
+    {% else %}
+    <a href="{{ static_prefix }}{{ crumb.url }}">{{ crumb.title }}</a>
+    {% endif %}
+    {% endfor %}
+</nav>

manual_src/templates/includes/head_meta.html

@@ -0,0 +1,14 @@
+{# retoor <retoor@molodetz.nl> #}
+<meta charset="UTF-8">
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<meta name="description" content="{{ seo.description|default(page_description)|default(site.description) }}">
+<meta name="keywords" content="{{ seo.keywords|default([])|join(', ') }}">
+<meta name="author" content="{{ site.author }}">
+
+<meta property="og:title" content="{{ seo.og_title|default(page_title ~ ' - ' ~ site.name) }}">
+<meta property="og:description" content="{{ seo.description|default(page_description)|default(site.description) }}">
+<meta property="og:type" content="{{ seo.og_type|default('website') }}">
+
+<meta name="twitter:card" content="summary">
+<meta name="twitter:title" content="{{ seo.og_title|default(page_title ~ ' - ' ~ site.name) }}">
+<meta name="twitter:description" content="{{ seo.description|default(page_description)|default(site.description) }}">

manual_src/templates/includes/page_footer.html

@@ -0,0 +1,11 @@
+{# retoor <retoor@molodetz.nl> #}
+<footer class="page-footer">
+    {% if prev_page %}
+    <a href="{{ static_prefix }}{{ prev_page.url }}" class="prev">{{ prev_page.title }}</a>
+    {% else %}
+    <span></span>
+    {% endif %}
+    {% if next_page %}
+    <a href="{{ static_prefix }}{{ next_page.url }}" class="next">{{ next_page.title }}</a>
+    {% endif %}
+</footer>

manual_src/templates/includes/search_box.html

@@ -0,0 +1,15 @@
+{# retoor <retoor@molodetz.nl> #}
+<div class="search-container" role="search">
+    <input type="text"
+           id="search-input"
+           placeholder="Search... (/)"
+           autocomplete="off"
+           aria-label="Search documentation"
+           aria-autocomplete="list"
+           aria-controls="search-results"
+           aria-expanded="false">
+    <div id="search-results"
+         class="search-dropdown"
+         role="listbox"
+         aria-label="Search results"></div>
+</div>

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>