fix(ui): show text-field focus as a neutral border, not a purple ring

Every text-entry control (Input, Textarea, Select and NativeSelect
triggers, the date and time fields, the calendar's dropdowns, the Coach
composer and the hand-built note fields) now marks focus by turning its
border the new neutral input-focus tone, about 5:1 on the dark
background and 4:1 on the light one, with no ring. A text field matches
:focus-visible on every mouse click, so the ring was on for everyone.
An invalid field keeps its red border and draws its destructive ring
only while focused. Buttons, links, checkboxes and switches keep their
rings.

text-field-focus-guard.test.ts fails when a text-field class string
brings a focus ring or a primary/ring-coloured focus border back.

src/app/globals.css

@@ -56,6 +56,7 @@
   --color-chart-1: var(--chart-1);
   --color-ring: var(--ring);
   --color-input: var(--input);
+  --color-input-focus: var(--input-focus);
   --color-border: var(--border);
   --color-destructive: var(--destructive);
   --color-accent-foreground: var(--accent-foreground);
@@ -241,6 +242,9 @@
   --destructive: #ff5555;
   --border: #44475a;
   --input: #44475a;
+  /* Text-field focus border: a neutral, foreground-based tone, no colour
+   * ring. ~5.2:1 on --background, ~6:1 on --card. */
+  --input-focus: #9a9b9d;
   --ring: #bd93f9;
   --chart-1: #bd93f9;
   --chart-2: #50fa7b;
@@ -369,6 +373,8 @@
   --success-foreground: #ffffff;
   --border: oklch(0.885 0.008 300);
   --input: oklch(0.87 0.009 300);
+  /* Text-field focus border, neutral: ~4.2:1 on --background. */
+  --input-focus: oklch(0.56 0.012 295);
   --ring: oklch(0.6 0.13 292);
   --chart-1: #644ac9;
   --chart-2: #14720a;