agent: drop orphaned button rules in agent.css (#394 follow-up)

After moving `↑ DASHB04RD` / `↻ R3BU1LD` / `↻ new session` into
the overflow `⋯` menu in #394, the per-button rules in agent.css
have no live consumer:

- `.btn-dashlink` (cyan back-link chip)
- `.btn-rebuild` (amber rebuild chip — note: the dashboard has
  its own `.btn-rebuild` for the per-row R3BU1LD form on the
  SW4RM tab, that stays)
- `.btn-new-session` (amber round-pill button)
- `.btn-send` (green send-button variant — orphaned since an
  earlier compose-form retirement, swept here)

Plus a comment-only `#state-row` block (layout fully provided by
the renamed `.agent-state-row` / `.agent-header-row` classes).

Each removed block is replaced with a one-line "moved to overflow"
comment so future readers don't reintroduce the old chrome by
mistake.

agent.css 23.6kb → 22.4kb.

frontend/packages/agent/src/agent.css

@@ -388,20 +388,14 @@ a:hover { color: var(--fg); text-shadow: 0 0 12px rgba(137, 220, 235, 0.9); }
 }
 .btn-login { color: var(--amber); border-color: var(--amber); }
 .btn-cancel { color: var(--red); border-color: var(--red); font-size: 0.85em; padding: 0.15em 0.6em; }
-.btn-rebuild {
+/* `.btn-rebuild` was the per-agent header chip — moved into the
-  color: var(--amber);
+   overflow menu in #394 (`.overflow-item-rebuild` covers it now).
-  border: 1px solid var(--amber);
+   The dashboard has its own `.btn-rebuild` rule for the per-row
-  padding: 0.15em 0.6em;
+   R3BU1LD form on the SW4RM tab; this one was specific to the
-  font-size: 0.55em;
+   per-agent header.
-  font-family: inherit;
+   `.btn-send` was a green send-button variant — orphaned since
-  text-decoration: none;
+   the dashboard's compose form was retired; no live consumer left
-  letter-spacing: 0.1em;
+   in either the agent or dashboard tree. */
-  margin-left: 0.6em;
-  vertical-align: middle;
-  cursor: pointer;
-}
-.btn-rebuild:hover { background: rgba(250, 179, 135, 0.1); }
-.btn-send { color: var(--green); border-color: var(--green); }
 .sendform { display: flex; gap: 0.6em; margin-top: 0.5em; }
 .sendform input {
   font-family: inherit; font-size: 1em;
@@ -431,9 +425,6 @@ pre.diff {
   word-break: break-all;
   max-height: 30em;
 }
-/* `#state-row` layout is provided by `.agent-state-row` /
-   `.agent-header-row` above (#394) — kept as a no-op selector
-   anchor in case any future rule needs to scope by id. */
 /* Per-agent inbox section — collapsible, dim, lives between the
    state row and the terminal so the operator can peek at what
    landed without scrolling through the live tail. */
@@ -572,21 +563,8 @@ pre.diff {
   text-shadow: 0 0 6px rgba(243, 139, 168, 0.55); }
 .status-badge.status-needs-login  { color: var(--amber);  border-color: var(--amber); }
 .status-badge.status-offline      { color: var(--muted);  border-color: var(--muted); }
-.btn-dashlink {
+/* Orphaned in #394 — `.btn-dashlink` chip beside the title moved
-  color: var(--cyan);
+   into the overflow menu (`.overflow-item-dashboard` covers it). */
-  border: 1px solid var(--cyan);
-  padding: 0.15em 0.6em;
-  font-size: 0.55em;
-  font-family: inherit;
-  text-decoration: none;
-  letter-spacing: 0.1em;
-  margin-left: 0.6em;
-  vertical-align: middle;
-}
-.btn-dashlink:hover {
-  background: rgba(137, 220, 235, 0.1);
-  box-shadow: 0 0 10px -2px currentColor;
-}
 .btn-cancel-turn {
   font-family: inherit;
   font-size: 0.8em;
@@ -604,27 +582,10 @@ pre.diff {
   background: rgba(243, 139, 168, 0.1);
   box-shadow: 0 0 10px -2px currentColor;
 }
-.btn-new-session {
+/* Orphaned in #394 — `.btn-new-session` round-pill moved into the
-  font-family: inherit;
+   overflow menu (`.overflow-item-new-session` covers it; the
-  font-size: 0.8em;
+   `:disabled` opacity treatment lives on the shared
-  letter-spacing: 0.08em;
+   `.overflow-item:disabled` rule). */
-  background: transparent;
-  color: var(--amber);
-  border: 1px solid var(--amber);
-  border-radius: 999px;
-  padding: 0.2em 0.8em;
-  cursor: pointer;
-  text-shadow: 0 0 4px currentColor;
-  transition: box-shadow 0.15s ease, background 0.15s ease;
-}
-.btn-new-session:hover {
-  background: rgba(250, 179, 135, 0.1);
-  box-shadow: 0 0 10px -2px currentColor;
-}
-.btn-new-session:disabled {
-  opacity: 0.4;
-  cursor: progress;
-}
 .state-badge {
   display: inline-block;
   padding: 0.25em 0.8em;