refactor(frontend): the last pay-down, part 1 — three dead views deleted, editor rules shared, .page-container + .fs-input canon, rules-shared.css; a one-declaration CSS body is not a shape (#2903, milestone 299 step 5)

The derive queue said the biggest duplicate families were whole views:
TaskViewerView, UserManagementView and LogsView were imported nowhere — left
behind when tasks moved to the editor and users/logs became SettingsView
tabs. Deleted (rule 22). Note/TaskEditorView carried six identical scoped
rules -> editor-shared.css (the .tag-suggest-row gap the scoped copies
actually rendered wins). Three views wrapped the page under three names ->
.page-container in components.css. Three scoped input recipes -> the design
system fs-input recipe (snippet #2336), verbatim, in components.css; width/
box-sizing stay with the caller. The three rules panes share .pane and the
pane heading via rules-shared.css (the auth-shared pattern, #2852).

Ledger: a single-declaration CSS rule keeps its selector in its fingerprint,
so `color: var(--fs-text-tertiary)` under five different names is no longer
a five-file "identical body" family — the first pay-down found that most of
the 148 dup families were exactly this, and nobody would consolidate them.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/views/SettingsView.vue

@@ -3172,7 +3172,7 @@ async function deleteUser(userId: number) {
 .cell-status { font-family: monospace; font-size: 0.85rem; }
 .cell-duration { color: var(--fs-text-tertiary); font-size: 0.8rem; white-space: nowrap; }
 .text-error { color: var(--fs-error); }
-/* Bare by design, like LogsView's twin of this: a `<tr>` has nothing to style
+/* Bare by design: a `<tr>` has nothing to style
    that its cells don't carry (#2444). */
 .detail-row td { padding: 0 0.75rem 0.75rem; border-bottom: 1px solid var(--fs-border-color); }
 .detail-ip { font-family: monospace; font-size: 0.8rem; color: var(--fs-text-tertiary); margin-bottom: 0.4rem; }