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/TaskEditorView.vue

@@ -823,16 +823,6 @@ useEditorGuards(dirty, save);
   gap: 0.75rem;
 }
 
-.body-tabs-row {
-  display: flex;
-  flex-direction: row;
-  align-items: center;
-  gap: 0.75rem;
-  flex-wrap: wrap;
-  padding-bottom: 0.5rem;
-  border-bottom: 1px solid var(--fs-border-color);
-}
-
 /* .task-main is a flex column; without flex-shrink: 0, long body content
    gets squeezed back to min-height and overflows visibly on top of siblings. */
 .body-editor-wrap,
@@ -840,10 +830,6 @@ useEditorGuards(dirty, save);
   flex-shrink: 0;
 }
 
-.body-editor-wrap {
-  min-height: 200px;
-}
-
 :deep(.preview-pane) {
   flex-shrink: 0;
 }
@@ -949,18 +935,6 @@ useEditorGuards(dirty, save);
   font-family: inherit;
 }
 .subtask-input:focus { outline: none; border-color: var(--fs-accent); }
-.stream-preview {
-  border: 1px solid var(--fs-border-color);
-  border-radius: var(--fs-radius-sm);
-  padding: 0.75rem;
-  background: var(--fs-surface-raised);
-  min-height: 200px;
-}
-.main-diff {
-  flex: 1;
-  min-height: 0;
-}
-
 /* Systems multi-select (in sidebar) */
 .sb-systems { display: flex; flex-direction: column; gap: 0.25rem; max-height: 160px; overflow-y: auto; }
 .sb-system-opt { display: flex; align-items: center; gap: 0.45rem; font-size: 0.85rem; color: var(--fs-text-primary); cursor: pointer; }
@@ -973,26 +947,11 @@ useEditorGuards(dirty, save);
   flex-direction: column;
   gap: 0.5rem;
 }
-.assist-section-title {
-  font-size: 0.78rem;
-  font-weight: 500;
-  color: var(--fs-text-secondary);
-  text-transform: uppercase;
-  letter-spacing: 0.05em;
-}
 .assist-actions {
   display: flex;
   gap: 0.4rem;
 }
 
-/* Tag suggest row inside sidebar */
-.tag-suggest-row {
-  display: flex;
-  flex-wrap: wrap;
-  gap: 0.3rem;
-  align-items: center;
-}
-
 /* Lifecycle timestamps */
 .sb-timestamps {
   display: flex;