fix(suggestion): stop generating mid-typing and let a pause bring a suggestion at once

With a 100 ms trigger left in the installed config, generation started in the
gaps between keystrokes; the next key ended the session silently, and that
session still counted against the 5 s minimum interval, so the moment the
user actually paused nothing came (rate-limited). The log showed a
generate-then-vanish cycle every 5-6 s.

The trigger delay now has a 500 ms floor and settings revision 6 resets a
stored value below it to 600 ms. A session ended because the user kept typing
no longer blocks the next request by the minimum interval (per-minute and
daily caps still apply), and that dismissal is logged.

apps/desktop/tests/main/services/input-flow-services.test.ts

@@ -477,7 +477,8 @@ describe('입력 플로우 서비스', () => {
       available: true,
       appName: 'Notion.exe',
       windowTitle: '회의록',
-      idleMs: 300,
+      // 멈춤 판단 하한(500ms)을 넘긴 멈춤
+      idleMs: 700,
       capturedAt: now,
       editedSinceFocus: true,
       typedRecently: true