canvas/{Schedule,Channels}Tab: fix accent-LIGHTER hover + Cancel no-op

Three button fixes — same AA-contrast-trap pattern shipped on
OnboardingWizard, MemoryTab, ConfirmDialog, ApprovalBanner.

ScheduleTab:
- Create/Update button: bg-accent-strong hover:bg-accent (accent is
  LIGHTER, drops below AA on white text) → bg-accent hover:bg-accent-
  strong + focus-visible ring.
- Cancel button: bg-surface-card hover:bg-surface-card no-op → hover
  surface-elevated + focus-visible ring.

ChannelsTab:
- Connect Channel button: same accent-LIGHTER trap → flipped + focus-
  visible ring.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

canvas/src/components/tabs/ChannelsTab.tsx

@@ -365,8 +365,12 @@ export function ChannelsTab({ workspaceId }: Props) {
             <p className="text-[10px] text-bad">{formError}</p>
           )}
           <button
+            type="button"
             onClick={handleCreate}
-            className="w-full text-xs py-1.5 rounded bg-accent-strong hover:bg-accent text-white transition"
+            // Was bg-accent-strong hover:bg-accent — accent is the
+            // LIGHTER variant; same AA contrast trap fixed in
+            // ScheduleTab/MemoryTab/OnboardingWizard.
+            className="w-full text-xs py-1.5 rounded bg-accent hover:bg-accent-strong text-white transition focus:outline-none focus-visible:ring-2 focus-visible:ring-accent/60 focus-visible:ring-offset-2 focus-visible:ring-offset-surface"
           >
             Connect Channel
           </button>

canvas/src/components/tabs/ScheduleTab.tsx

@@ -269,15 +269,23 @@ export function ScheduleTab({ workspaceId }: Props) {
           {error && <div className="text-[10px] text-bad">{error}</div>}
           <div className="flex gap-2">
             <button
+              type="button"
               onClick={handleSubmit}
               disabled={!formCron || !formPrompt}
-              className="text-[11px] px-3 py-1 bg-accent-strong text-white rounded hover:bg-accent disabled:opacity-40 transition-colors"
+              // Was bg-accent-strong hover:bg-accent — accent is the
+              // LIGHTER variant, so this hovered lighter on white text
+              // and dropped contrast below AA. Same trap fixed in
+              // OnboardingWizard, ConfirmDialog, ApprovalBanner.
+              className="text-[11px] px-3 py-1 bg-accent text-white rounded hover:bg-accent-strong disabled:opacity-40 transition-colors focus:outline-none focus-visible:ring-2 focus-visible:ring-accent/60 focus-visible:ring-offset-1 focus-visible:ring-offset-surface"
             >
               {editId ? "Update" : "Create"}
             </button>
             <button
+              type="button"
               onClick={resetForm}
-              className="text-[11px] px-3 py-1 bg-surface-card text-ink-mid rounded hover:bg-surface-card transition-colors"
+              // Was hover:bg-surface-card on top of bg-surface-card —
+              // silent no-op hover. Lift to surface-elevated.
+              className="text-[11px] px-3 py-1 bg-surface-card text-ink-mid rounded hover:bg-surface-elevated hover:text-ink transition-colors focus:outline-none focus-visible:ring-2 focus-visible:ring-accent/40 focus-visible:ring-offset-1 focus-visible:ring-offset-surface"
             >
               Cancel
             </button>