feat: replace admin auth with cookie-based profile picker

Remove all authentication (login, sessions, bcrypt, itsdangerous) since
the app runs on a private homelab LAN. Replace with a profile picker
landing page and cookie-based profile selection (1-year expiry).

- Add Alembic migration to drop password_hash/is_admin columns
- Delete auth service, auth routes, login template, and auth tests
- Rewrite app/utils/auth.py with NoProfileSelectedError and
  require_active_profile dependency
- Add profile creation flow (GET/POST /profiles/create)
- Rewrite home page as profile picker with card layout
- Update all route files to use profile dependency instead of admin auth
- Remove bcrypt and itsdangerous from requirements
- Remove admin_username/admin_password from config
- Update all tests for new profile-based access model

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/templates/pages/profile_create.html

@@ -0,0 +1,46 @@
+{% extends "base.html" %}
+
+{% block title %}SneakySwole — Create Profile{% endblock %}
+
+{% block content %}
+<hgroup>
+    <h1>Create Profile</h1>
+    <p>Set up a new workout profile</p>
+</hgroup>
+
+{% if error %}
+<article aria-label="Error" class="pico-background-red-500">
+    <p>{{ error }}</p>
+</article>
+{% endif %}
+
+<form method="POST" action="/profiles/create">
+    <label for="display_name">
+        Display Name <span aria-hidden="true">*</span>
+        <input type="text" id="display_name" name="display_name" required
+               placeholder="e.g. Phillip" value="{{ request.query_params.get('display_name', '') }}">
+    </label>
+
+    <label for="height">
+        Height
+        <input type="text" id="height" name="height"
+               placeholder="e.g. 6'0&quot;">
+    </label>
+
+    <label for="weight">
+        Weight
+        <input type="text" id="weight" name="weight"
+               placeholder="e.g. 260 lbs">
+    </label>
+
+    <label for="goals">
+        Goals
+        <textarea id="goals" name="goals" rows="3"
+                  placeholder="e.g. Build strength, improve mobility"></textarea>
+    </label>
+
+    <button type="submit">Create Profile</button>
+</form>
+
+<p><a href="/">&larr; Back to profiles</a></p>
+{% endblock %}