feat: center section divider to match table width (#2698)

The '========== Updated Releases ==========' header was a fixed 38
chars regardless of the table width below it. Now the divider line
is extended to match the table's visual width, with the title text
centered within the '=' borders.

- Add TableVisualWidth() to measure table width via runewidth
- Add HeaderDividerCentered() and HeaderDividerCenteredStyled()
  for centered dividers with optional bold+blue ANSI styling
- Refactor DisplayAffectedReleases to build the table first, then
  compute its width before logging the header
- Update all test snapshots and integration test output files

Signed-off-by: yxxhero <aiopsclub@163.com>

pkg/app/testdata/testdestroy/destroy_installed_but_disabled_release/log

@@ -13,7 +13,7 @@ release "frontend-v1" processed
 processing releases in group 2/2: default//backend-v1
 release "backend-v1" processed
 
-========== Deleted Releases ==========
+======== Deleted Releases ========
 NAME          NAMESPACE   DURATION
 frontend-v1                     0s
 backend-v1                      0s

pkg/app/testdata/testdestroy/destroy_only_one_release_with_selector/log

@@ -8,7 +8,7 @@ GROUP RELEASES
 processing releases in group 1/1: default//logging
 release "logging" processed
 
-========== Deleted Releases ==========
+====== Deleted Releases ======
 NAME      NAMESPACE   DURATION
 logging                     0s
 

pkg/app/testdata/testdestroy/helm3/log

@@ -13,7 +13,7 @@ release "frontend-v1" processed
 processing releases in group 2/2: default//backend-v1
 release "backend-v1" processed
 
-========== Deleted Releases ==========
+======== Deleted Releases ========
 NAME          NAMESPACE   DURATION
 frontend-v1                     0s
 backend-v1                      0s

pkg/app/testdata/testdestroy/smoke/log

@@ -25,7 +25,7 @@ processing releases in group 5/5: default//front-proxy, default//logging
 release "front-proxy" processed
 release "logging" processed
 
-========== Deleted Releases ==========
+========= Deleted Releases ==========
 NAME             NAMESPACE   DURATION
 frontend-v3                        0s
 frontend-v2                        0s