Added deprecation markers for class, object and profile page | Also includes bugfix for extension attribute selections

[floydtree]

1. Deprecated attributes notice on detail pages

• Added has_deprecated_attributes?/1 and deprecated_attributes_count/1 helpers to page_view.ex
• Class, object, and profile detail pages now show a notice banner when they contain deprecated attributes, with the count and a prompt to check "Show deprecated items"

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2. Profiles link in top navigation

• Added "Profiles" nav item between "Objects" and "Observable" in the top header bar

3. Extension filtering fix

• JS (app.js): build_url_params now always includes extensions= in the URL, even when empty, so the server can distinguish "no extensions selected" from "param not provided"
• Server (page_controller.ex): All page actions (classes, objects, dictionary, profiles, category_by_id) now default extensions to "" when the param is missing, ensuring core-only filtering on direct page loads

4. Extension params retained on content navigation

• Content links in .main-page (class, object, category, profile, dictionary paths) now get extension/profile params appended on page load, so navigating into a class/object preserves the selected extensions in the URL