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/assets/components.css

@@ -297,3 +297,36 @@
   background: var(--fs-action-destructive-hover);
   border-color: var(--fs-action-destructive-hover);
 }
+
+/* ── Page container ─────────────────────────────────────────────────────────
+   The one wrapper a top-level view sits in: page width from the layout
+   tokens, centred, clipped horizontally so a wide child (a kanban, a table)
+   scrolls inside itself instead of the page. ProjectListView, ProjectView and
+   SnippetListView each carried this rule under their own name until #2903
+   (milestone 299). */
+.page-container {
+  max-width: var(--fs-layout-page-max);
+  margin: 2rem auto;
+  padding: 0 var(--fs-layout-page-pad);
+  overflow-x: clip;
+}
+
+/* ── Form input (fs-surfaces, snippet #2336) ────────────────────────────────
+   Inputs sit DARKER than the page they're on — an inset well rather than a
+   raised panel; that inversion is what makes a field read as writable. The
+   design system's recipe, verbatim; width/box-sizing stay the caller's
+   (an inline select and a full-width textarea differ there). Three scoped
+   copies of an older input recipe were folded into this in #2903. */
+.fs-input {
+  background: var(--fs-surface-page);
+  border: var(--fs-border);
+  border-radius: var(--fs-radius-md);
+  padding: var(--fs-space-2) var(--fs-space-3);   /* 8px 12px */
+  color: var(--fs-text-primary);
+  font-family: var(--fs-font-body);
+  font-size: var(--fs-size-body);
+  transition: box-shadow var(--fs-dur-fast) var(--fs-ease);
+}
+.fs-input::placeholder { color: var(--fs-text-tertiary); }
+.fs-input:focus { outline: none; box-shadow: var(--fs-focus-ring); }
+.fs-input:disabled { opacity: var(--fs-disabled-opacity); cursor: not-allowed; }