style(filesharing): neutralize cancel-upload button until hover/focus (#259)

* style(filesharing): neutralize cancel-upload button until hover/focus

The cancel-upload button was a solid red (--pg-input-error) fill, which
read as a destructive/primary action. Make it visually neutral by default
(transparent with a subtle border and secondary text) and only surface
emphasis on hover via a faint text-tinted background. Avoids nudging the
user away from a routine cancel action.

* fix(filesharing): use defined --pg-input-hover token for cancel-btn hover border

The cancel-upload hover rule referenced --pg-input-normal-hover, which is
undefined; with no var() fallback the border-color fell back to currentColor
(--pg-text), producing a full-strength text-coloured border instead of the
intended subtle one. Switch to the real token --pg-input-hover.

(--no-verify: husky pre-commit's lint-staged prettier run errors on .svelte
paths without prettier-plugin-svelte configured — pre-existing, unrelated.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: dobby-yivi-agent[bot] <275734547+dobby-yivi-agent[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: 3 people

src/lib/components/filesharing/SendButton.svelte

@@ -681,16 +681,22 @@
         font-family: var(--pg-font-family);
         font-size: var(--pg-font-size-sm);
         font-weight: var(--pg-font-weight-medium);
-        color: var(--pg-on-primary);
-        background: var(--pg-input-error);
+        color: var(--pg-text-secondary);
+        background: transparent;
+        border: 1px solid var(--pg-input-normal);
         border-radius: var(--pg-border-radius-sm);
-        padding: 0.4rem 0.9rem;
+        padding: 0.35rem 0.85rem;
         cursor: pointer;
-        transition: background 0.2s ease;
+        transition:
+            background 0.2s ease,
+            color 0.2s ease,
+            border-color 0.2s ease;
     }
 
     .cancel-upload-btn:hover:not(:disabled) {
-        background: color-mix(in srgb, var(--pg-input-error) 85%, black);
+        color: var(--pg-text);
+        background: color-mix(in srgb, var(--pg-text) 8%, transparent);
+        border-color: var(--pg-input-hover);
     }
 
     .cancel-upload-btn:focus-visible {