fix: 't' key tag editing on fresh entries and allow last-tag removal

[manato-tajiri]

Description

This PR fixes two bugs related to the t key tag editing feature:

Bug 1: t key silently fails on fresh entries (never edited via e)

Root cause: In handlers.go:411, the showEditTagsForm save callback discards the error from UpdateServer with _ = t.serverService.UpdateServer(...). If the SSH config write fails (e.g., permissions issue), the tags are never saved but the UI shows "Tags updated" as if it succeeded.

Fix: The error is now properly surfaced via an error modal, matching the behavior of handleServerSave (used by the e key).

Bug 2: Selection jumps to first entry after tag save

Root cause: In server_list.go:85, UpdateServers always resets the selected item to index 0 after refreshing the list, making it appear that tags were not saved on the edited server.

Fix: UpdateServers now tracks the currently selected server alias before refresh and restores the selection to that same server afterward.

Notes

• The nil-guard fix in metadata_manager.go (for clearing the last tag) was already present in the codebase — no changes needed there.
• All existing tests pass.

Closes #(issue if applicable)

[manato-tajiri]

Hi @Adembc — this PR fixes two bugs in the tag editing flow (t key):

1. handlers.go:411: The error from UpdateServer is silently discarded (_ = ...). If the SSH config write fails, tags are never saved but the UI says "Tags updated." Fixed by surfacing errors via a modal (matching handleServerSave behavior used by the e key).

2. server_list.go:85: UpdateServers resets selection to index 0 after every refresh, making it appear tags weren't saved on the edited server. Fixed by tracking the current server alias and restoring selection after refresh.

CC: I've also filed issue #116 documenting this bug from a user report. Would appreciate a review when you have a moment.