refactor(ui): four UI/navigation hygiene fixes from module-by-module re-review

- popper-config.el: move `(popper-mode +1)` and `(popper-echo-mode
  +1)` from the use-package `:init` block into `:config`.
  `:disabled t' on use-package skips `:config' but still runs
  `:init', so the previous shape enabled popper-mode on every load,
  including batch / test runs, despite the disabled marker.

- modeline-config.el: make `cj/modeline-vc-fetch' fall back when
  the internal `vc-git--symbolic-ref' is missing.  `require' uses
  `nil 'noerror', the call sits inside an `fboundp' guard, and
  `ignore-errors' wraps the call itself so an Emacs version that
  renames or removes the accessor leaves `branch' at
  `vc-working-revision''s output instead of crashing the modeline.

- ui-config.el: guard the cursor-color `post-command-hook' behind
  `(display-graphic-p)' both at install time and inside the
  function body.  Batch / TTY runs short-circuit cleanly with no
  per-command overhead.  A `server-after-make-frame-hook' catches
  the daemon case where the first GUI frame is created after
  ui-config loads and installs the hook lazily.  Updates
  test-ui-config--buffer-cursor-state and
  test-ui-cursor-color-integration to stub `display-graphic-p' so
  the work body still runs under batch.

- nerd-icons-config.el: drop `:demand t' (`:defer t' now), keeping
  the `:config' advice install as the natural lazy-on-load path.
  Add a `with-eval-after-load 'nerd-icons' block as a safety net for
  the already-loaded case on re-eval; the block uses `advice-member-p'
  so the advice never stacks.

1 files changed, 5 insertions, 2 deletions

diff --git a/tests/test-ui-config--buffer-cursor-state.el b/tests/test-ui-config--buffer-cursor-state.el
index add0d030..ead05741 100644
--- a/tests/test-ui-config--buffer-cursor-state.el
+++ b/tests/test-ui-config--buffer-cursor-state.el
@@ -72,7 +72,9 @@ buffer the user navigates, so `read-only' (orange) is kept."
 
 (ert-deftest test-ui-config-set-cursor-color-live-vterm-not-orange ()
   "Normal: in a live vterm the cursor-color hook picks a writeable color,
-not the read-only orange -- even though the vterm buffer is read-only."
+not the read-only orange -- even though the vterm buffer is read-only.
+`display-graphic-p' is stubbed t so the function reaches its work body
+in batch mode (the live function no-ops on TTY frames by design)."
   (let ((buf (cj/test--make-fake-vterm-buffer "*test-vterm-cursor-color*"))
         (applied 'unset))
     (unwind-protect
@@ -81,7 +83,8 @@ not the read-only orange -- even though the vterm buffer is read-only."
           (setq-local vterm-copy-mode nil)
           (let ((cj/-cursor-last-color nil)
                 (cj/-cursor-last-buffer nil))
-            (cl-letf (((symbol-function 'set-cursor-color)
+            (cl-letf (((symbol-function 'display-graphic-p) (lambda () t))
+                      ((symbol-function 'set-cursor-color)
                        (lambda (c) (setq applied c))))
               (cj/set-cursor-color-according-to-mode)))
           (should (stringp applied))