swarm-ui: fix inconsistent header icons + body edge gap

LinksMenu and SettingsMenu triggers mixed a full-colour emoji (link)
with a plain text glyph (gear) - different rendering paths mean
different, unfixable sizes/styles. Replace both with matching inline
SVG icons (feather/lucide gear + link glyphs), same viewBox/stroke/
size, so the two buttons finally share one rendering path.

Also: shared base.css never zeroed the default UA body margin, which
showed as a bg-coloured strip around the whole viewport edge on any
full-bleed header (swarm-uis .shell-header among them). Zeroed it in
the shared file so every consumer (dashboard, agent UI, swarm-ui) gets
the fix, not just swarm-ui.

Screenshot-verified at both desktop and phone widths.

frontend/packages/shared/src/base.css

@@ -6,6 +6,16 @@
    top of this and must NOT redeclare the colour variables; `theme.css`
    is the one source of truth. */
 body {
+  /* The default UA stylesheet gives `body` an 8px margin — every page
+     using this shared base had it as a `--bg`-coloured strip visible
+     around the whole viewport edge, e.g. left/right of any full-bleed
+     header (swarm-ui's `.shell-header`, `--bg-elev`, doesn't actually
+     reach the real viewport edge without this). Reported live as
+     "small bg colored gap left and right of the header" (reported live
+     by mara).
+     Zeroed here since every page linking this file wants full-bleed
+     chrome, not a browser default nobody asked for. */
+  margin: 0;
   background: var(--bg);
   color: var(--fg);
   font-family: "JetBrains Mono", "Fira Code", "Cascadia Code", "Source Code Pro", monospace;

frontend/packages/swarm-ui/src/shell/LinksMenu.tsx

@@ -62,7 +62,30 @@ export function LinksMenu() {
         aria-label="swarm services"
         onClick={() => setOpen((v) => !v)}
       >
-        🔗
+        {/* Feather/lucide "link" glyph, not the 🔗 emoji this replaced —
+            reported live by mara: "links and settings icon styles
+            different / all different sizes". An emoji glyph is rendered
+            by the
+            OS/browser's colour-emoji font at that font's own fixed
+            metrics, ignoring `font-size`/`color` — it can never match a
+            neighbouring text-style icon (SettingsMenu's `⚙`) in size or
+            weight, on any platform. Same inline-SVG shape as
+            SettingsMenu's gear now uses, so both trigger buttons finally
+            share one rendering path (stroke, viewBox, size). */}
+        <svg
+          width="1.3em"
+          height="1.3em"
+          viewBox="0 0 24 24"
+          fill="none"
+          stroke="currentColor"
+          stroke-width="2"
+          stroke-linecap="round"
+          stroke-linejoin="round"
+          aria-hidden="true"
+        >
+          <path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71" />
+          <path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71" />
+        </svg>
       </button>
       {open ? (
         <div class="links-menu-popover" role="menu">

frontend/packages/swarm-ui/src/shell/SettingsMenu.tsx

@@ -50,7 +50,28 @@ export function SettingsMenu() {
         aria-label="settings"
         onClick={() => setOpen((v) => !v)}
       >
-        ⚙
+        {/* Feather/lucide "settings" glyph, not the bare `⚙` character —
+            reported live by mara: icon styles/sizes inconsistent between
+            this button and LinksMenu's. `⚙` is a plain text glyph so it does
+            scale with `font-size`/`color`, but its exact shape and
+            optical weight are down to whatever font the browser
+            substitutes for that one codepoint — not guaranteed to match
+            an SVG icon at all, which is what LinksMenu's link glyph is
+            now built from too. One shared rendering path for both. */}
+        <svg
+          width="1.3em"
+          height="1.3em"
+          viewBox="0 0 24 24"
+          fill="none"
+          stroke="currentColor"
+          stroke-width="2"
+          stroke-linecap="round"
+          stroke-linejoin="round"
+          aria-hidden="true"
+        >
+          <circle cx="12" cy="12" r="3" />
+          <path d="M19.4 15a1.65 1.65 0 0 0 .33 1.82l.06.06a2 2 0 1 1-2.83 2.83l-.06-.06a1.65 1.65 0 0 0-1.82-.33 1.65 1.65 0 0 0-1 1.51V21a2 2 0 0 1-4 0v-.09A1.65 1.65 0 0 0 9 19.4a1.65 1.65 0 0 0-1.82.33l-.06.06a2 2 0 1 1-2.83-2.83l.06-.06a1.65 1.65 0 0 0 .33-1.82 1.65 1.65 0 0 0-1.51-1H3a2 2 0 0 1 0-4h.09A1.65 1.65 0 0 0 4.6 9a1.65 1.65 0 0 0-.33-1.82l-.06-.06a2 2 0 1 1 2.83-2.83l.06.06a1.65 1.65 0 0 0 1.82.33H9a1.65 1.65 0 0 0 1-1.51V3a2 2 0 0 1 4 0v.09a1.65 1.65 0 0 0 1 1.51 1.65 1.65 0 0 0 1.82-.33l.06-.06a2 2 0 1 1 2.83 2.83l-.06.06a1.65 1.65 0 0 0-.33 1.82V9a1.65 1.65 0 0 0 1.51 1H21a2 2 0 0 1 0 4h-.09a1.65 1.65 0 0 0-1.51 1z" />
+        </svg>
       </button>
       {open ? (
         <div class="settings-menu-popover" role="menu">