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/home.html

@@ -8,5 +8,33 @@
     <p>Your open-source workout tracker</p>
 </hgroup>
 
-<p>Welcome to SneakySwole. Get started by logging in.</p>
+{% if profiles %}
+<h2>Select Profile</h2>
+<div class="grid">
+    {% for profile in profiles %}
+    <article>
+        <header>
+            <strong>{{ profile.display_name }}</strong>
+        </header>
+        {% if profile.height or profile.weight %}
+        <p>
+            {% if profile.height %}Height: {{ profile.height }}{% endif %}
+            {% if profile.height and profile.weight %} &middot; {% endif %}
+            {% if profile.weight %}Weight: {{ profile.weight }}{% endif %}
+        </p>
+        {% endif %}
+        <footer>
+            <form method="POST" action="/profiles/switch">
+                <input type="hidden" name="profile_id" value="{{ profile.id }}">
+                <button type="submit" class="contrast">Select</button>
+            </form>
+        </footer>
+    </article>
+    {% endfor %}
+</div>
+{% else %}
+<p>No profiles yet. Create one to get started.</p>
+{% endif %}
+
+<a href="/profiles/create" role="button" class="secondary">Create New Profile</a>
 {% endblock %}

app/templates/pages/login.html

@@ -1,27 +0,0 @@
-{% extends "base.html" %}
-
-{% block title %}SneakySwole — Login{% endblock %}
-
-{% block content %}
-<article>
-    <header>
-        <h2>Admin Login</h2>
-    </header>
-
-    {% if error %}
-    <div class="flash-error" role="alert">{{ error }}</div>
-    {% endif %}
-
-    <form method="POST" action="/login">
-        <label for="username">Username</label>
-        <input type="text" id="username" name="username"
-               placeholder="Enter username" required autofocus>
-
-        <label for="password">Password</label>
-        <input type="password" id="password" name="password"
-               placeholder="Enter password" required>
-
-        <button type="submit">Login</button>
-    </form>
-</article>
-{% endblock %}

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 %}