add app.css with reset and design tokens

introduce a single shared stylesheet under public/css. this first
section covers a minimal reset, warm/readable design tokens (color,
typography, spacing, radii, shadows), and base element styling for
headings, links, lists, forms, and buttons. layout primitives and
component classes follow in subsequent commits.

public/css/app.css

@@ -0,0 +1,218 @@
+/* =========================================================================
+   Daily Goals - app.css
+   Single shared stylesheet. Sectioned for readability.
+   ========================================================================= */
+
+/* -------------------------------------------------------------------------
+   1. Reset
+   ------------------------------------------------------------------------- */
+
+*,
+*::before,
+*::after {
+    box-sizing: border-box;
+}
+
+html,
+body {
+    margin: 0;
+    padding: 0;
+}
+
+img,
+svg {
+    display: block;
+    max-width: 100%;
+}
+
+button {
+    font: inherit;
+    color: inherit;
+    cursor: pointer;
+}
+
+input,
+textarea,
+select {
+    font: inherit;
+    color: inherit;
+}
+
+/* -------------------------------------------------------------------------
+   2. Design tokens
+   ------------------------------------------------------------------------- */
+
+:root {
+    /* Color: warm, readable palette */
+    --color-bg: #faf7f2;
+    --color-surface: #ffffff;
+    --color-surface-alt: #f3ede2;
+    --color-text: #2b2622;
+    --color-text-muted: #6b5d52;
+    --color-primary: #5a7a4f;
+    --color-primary-hover: #486340;
+    --color-accent: #8a5a3b;
+    --color-accent-hover: #6f4730;
+    --color-border: #e3dccf;
+    --color-border-strong: #c9bfae;
+    --color-danger: #a94442;
+    --color-success: #4f7a5a;
+
+    /* Typography */
+    --font-serif: Georgia, "Iowan Old Style", "Source Serif Pro", serif;
+    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui,
+        sans-serif;
+    --font-size-base: 1rem;
+    --font-size-sm: 0.875rem;
+    --font-size-lg: 1.125rem;
+    --font-size-h1: 2rem;
+    --font-size-h2: 1.5rem;
+    --font-size-h3: 1.25rem;
+    --line-height-base: 1.6;
+    --line-height-tight: 1.25;
+
+    /* Spacing scale */
+    --space-1: 0.25rem;
+    --space-2: 0.5rem;
+    --space-3: 0.75rem;
+    --space-4: 1rem;
+    --space-5: 1.5rem;
+    --space-6: 2rem;
+    --space-7: 3rem;
+
+    /* Layout */
+    --max-width: 42rem;
+    --max-width-wide: 60rem;
+
+    /* Radii */
+    --radius-sm: 4px;
+    --radius-md: 8px;
+    --radius-lg: 12px;
+
+    /* Shadows */
+    --shadow-sm: 0 1px 2px rgba(43, 38, 34, 0.06);
+    --shadow-md: 0 4px 12px rgba(43, 38, 34, 0.1);
+    --shadow-lg: 0 12px 32px rgba(43, 38, 34, 0.18);
+
+    /* Transitions */
+    --transition-fast: 120ms ease;
+    --transition-base: 200ms ease;
+}
+
+/* -------------------------------------------------------------------------
+   3. Base elements
+   ------------------------------------------------------------------------- */
+
+body {
+    background-color: var(--color-bg);
+    color: var(--color-text);
+    font-family: var(--font-sans);
+    font-size: var(--font-size-base);
+    line-height: var(--line-height-base);
+    -webkit-font-smoothing: antialiased;
+    text-rendering: optimizeLegibility;
+}
+
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
+    font-family: var(--font-serif);
+    font-weight: 600;
+    line-height: var(--line-height-tight);
+    margin: 0;
+    color: var(--color-text);
+}
+
+h1 {
+    font-size: var(--font-size-h1);
+}
+
+h2 {
+    font-size: var(--font-size-h2);
+}
+
+h3 {
+    font-size: var(--font-size-h3);
+}
+
+p {
+    margin: 0;
+}
+
+a {
+    color: var(--color-accent);
+    text-decoration: none;
+    transition: color var(--transition-fast);
+}
+
+a:hover,
+a:focus {
+    color: var(--color-accent-hover);
+    text-decoration: underline;
+}
+
+ul,
+ol {
+    margin: 0;
+    padding: 0;
+    list-style: none;
+}
+
+label {
+    display: block;
+    font-size: var(--font-size-sm);
+    color: var(--color-text-muted);
+    font-weight: 500;
+}
+
+input[type="text"],
+input[type="email"],
+input[type="password"],
+input[type="date"],
+input[type="number"],
+textarea,
+select {
+    display: block;
+    width: 100%;
+    margin-top: var(--space-1);
+    padding: var(--space-2) var(--space-3);
+    background-color: var(--color-surface);
+    color: var(--color-text);
+    border: 1px solid var(--color-border-strong);
+    border-radius: var(--radius-sm);
+    transition: border-color var(--transition-fast),
+        box-shadow var(--transition-fast);
+}
+
+input:focus,
+textarea:focus,
+select:focus {
+    outline: none;
+    border-color: var(--color-primary);
+    box-shadow: 0 0 0 3px rgba(90, 122, 79, 0.15);
+}
+
+button {
+    display: inline-block;
+    padding: var(--space-2) var(--space-4);
+    background-color: var(--color-surface);
+    color: var(--color-text);
+    border: 1px solid var(--color-border-strong);
+    border-radius: var(--radius-sm);
+    font-weight: 500;
+    transition: background-color var(--transition-fast),
+        border-color var(--transition-fast), color var(--transition-fast);
+}
+
+button:hover,
+button:focus {
+    background-color: var(--color-surface-alt);
+    border-color: var(--color-text-muted);
+}
+
+form {
+    margin: 0;
+}