feat(m5d): demand-driven deep backfill + per-user ETA

Per-user opt-in to full-history (deep) backfill so a new user's unique
channels no longer trigger a big shared-quota burst.

- migration 0007: Subscription.deep_requested (default false); seed admins'
  existing subscriptions to preserve today's global-backfill behaviour
- run_deep_backfill is now demand-driven: only channels at least one user has
  requested are deep-backfilled; recent backfill stays unconditional (cheap)
- estimate_deep_backfill ETA helper (quota-bound) surfaced in /api/sync/my-status
- POST /api/sync/deep-all to opt all my channels in; PATCH channels accepts
  deep_requested
- UI: per-channel Full history toggle, Backfill everything action, deep
  progress + ETA in Channels header and Settings - Sync

frontend/src/components/Channels.tsx

@@ -5,12 +5,14 @@ import {
   ArrowUp,
   Eye,
   EyeOff,
+  History,
   Plus,
   RefreshCw,
   Search,
   X,
 } from "lucide-react";
 import { api, type ManagedChannel, type Tag } from "../lib/api";
+import { formatEta } from "../lib/format";
 import { notify } from "../lib/notifications";
 import Tooltip from "./Tooltip";
 
@@ -35,8 +37,10 @@ export default function Channels({
   const userTags = (tagsQuery.data ?? []).filter((t) => !t.system);
 
   const patch = useMutation({
-    mutationFn: (v: { id: string; body: { priority?: number; hidden?: boolean } }) =>
-      api.updateChannel(v.id, v.body),
+    mutationFn: (v: {
+      id: string;
+      body: { priority?: number; hidden?: boolean; deep_requested?: boolean };
+    }) => api.updateChannel(v.id, v.body),
     onSuccess: () => qc.invalidateQueries({ queryKey: ["channels"] }),
   });
   const attach = useMutation({
@@ -66,6 +70,18 @@ export default function Channels({
     mutationFn: (id: number) => api.deleteTag(id),
     onSuccess: () => invalidate(),
   });
+  const deepAll = useMutation({
+    mutationFn: () => api.deepAll(true),
+    onSuccess: (r: { updated?: number }) => {
+      qc.invalidateQueries({ queryKey: ["channels"] });
+      qc.invalidateQueries({ queryKey: ["my-status"] });
+      notify({
+        level: "success",
+        message: `Full history requested for ${r.updated ?? 0} channels`,
+      });
+    },
+    onError: () => notify({ level: "error", message: "Couldn't request full history" }),
+  });
 
   const channels = (channelsQuery.data ?? []).filter(
     (c) => !q || (c.title ?? "").toLowerCase().includes(q.toLowerCase())
@@ -85,9 +101,16 @@ export default function Channels({
           />
           <Stat
             label="Full history"
-            value={`${s.channels_deep_done}/${s.channels_total}`}
-            hint="Channels whose entire back-catalog is fetched. The rest backfill gradually."
+            value={`${s.channels_deep_done}/${s.channels_deep_requested}`}
+            hint="Channels whose entire back-catalog is fetched, out of the ones you've requested full history for."
           />
+          {s.deep_pending_count > 0 && (
+            <Stat
+              label="left"
+              value={formatEta(s.deep_eta_seconds)}
+              hint={`Rough estimate to finish full-history backfill of ${s.deep_pending_count} pending channel(s), based on the shared daily quota.`}
+            />
+          )}
           <Stat label="My videos" value={s.my_videos.toLocaleString()} hint="Total videos available across your channels." />
           <Stat
             label="Quota left"
@@ -121,6 +144,19 @@ export default function Channels({
             Sync subscriptions
           </button>
         </Tooltip>
+        <Tooltip
+          side="bottom"
+          hint="Request full back-catalog backfill for every channel you're subscribed to. Older videos and search become complete as the shared daily quota allows — this can take a while."
+        >
+          <button
+            onClick={() => deepAll.mutate()}
+            disabled={deepAll.isPending}
+            className="glass-card glass-hover flex items-center gap-2 px-3 py-2 rounded-xl text-sm disabled:opacity-50 transition"
+          >
+            <History className={`w-4 h-4 ${deepAll.isPending ? "animate-pulse" : ""}`} />
+            Backfill everything
+          </button>
+        </Tooltip>
       </div>
 
       <p className="text-xs text-muted mb-4 leading-relaxed">
@@ -181,6 +217,9 @@ export default function Channels({
               onView={() => onViewChannel(c.id, c.title ?? "This channel")}
               onPriority={(d) => patch.mutate({ id: c.id, body: { priority: c.priority + d } })}
               onHide={() => patch.mutate({ id: c.id, body: { hidden: !c.hidden } })}
+              onDeep={() =>
+                patch.mutate({ id: c.id, body: { deep_requested: !c.deep_requested } })
+              }
               onToggleTag={(tagId) =>
                 c.tag_ids.includes(tagId)
                   ? detach.mutate({ id: c.id, tagId })
@@ -232,6 +271,7 @@ function ChannelRow({
   onView,
   onPriority,
   onHide,
+  onDeep,
   onToggleTag,
 }: {
   c: ManagedChannel;
@@ -239,6 +279,7 @@ function ChannelRow({
   onView: () => void;
   onPriority: (delta: number) => void;
   onHide: () => void;
+  onDeep: () => void;
   onToggleTag: (tagId: number) => void;
 }) {
   return (
@@ -279,11 +320,29 @@ function ChannelRow({
             label="recent"
             hint={c.recent_synced ? "Recent uploads synced." : "Recent uploads not fetched yet."}
           />
-          <SyncBadge
-            ok={c.backfill_done}
-            label="full"
-            hint={c.backfill_done ? "Full history fetched." : "Only recent videos so far; full history pending."}
-          />
+          {c.backfill_done ? (
+            <SyncBadge ok label="full" hint="Full history fetched." />
+          ) : (
+            <Tooltip
+              hint={
+                c.deep_requested
+                  ? "Full history requested — this channel's whole back-catalog will backfill as the shared quota allows. Click to cancel the request."
+                  : "Only recent uploads so far. Click to request this channel's full back-catalog (older videos + complete search)."
+              }
+            >
+              <button
+                onClick={onDeep}
+                className={`inline-flex items-center gap-1 text-[10px] px-1.5 py-0.5 rounded-full border transition ${
+                  c.deep_requested
+                    ? "bg-accent text-accent-fg border-accent"
+                    : "bg-card border-border text-muted hover:border-accent"
+                }`}
+              >
+                <History className="w-3 h-3" />
+                {c.deep_requested ? "full history queued" : "get full history"}
+              </button>
+            </Tooltip>
+          )}
           {userTags.map((t) => {
             const on = c.tag_ids.includes(t.id);
             return (