feat: convert file manager into a plugin

packages/plugin-sdk/FINISH-LIST.md

@@ -23,14 +23,16 @@ it's done.
   is the SDK copy fleets now uses; core's copy was left in place rather than
   turned into a re-export, since host-metrics's own conversion step is where
   its imports should move wholesale. Owner: host-metrics's Phase B step.
-- **B5 (proxmox):** `useConnectionRetry`, `runAdaptivePolling` and `cn` are
-  duplicated in `plugins/proxmox/src/frontend/stats/` rather than shared with
-  core's `src/ui/lib/` originals, matching the same "add to the SDK once a
-  second plugin needs it" call B3 made for `ManagerCardShell`. host-metrics's
-  own conversion needs the same two hooks for its stats tab, so promote both
-  into `@termix/plugin-sdk/frontend` (and `cn` into `@termix/plugin-sdk/ui`)
-  the next time either is touched. Owner: D1, or host-metrics's Phase B step
-  if it lands first.
+- **B5 (proxmox):** `runAdaptivePolling` and `cn` are duplicated in
+  `plugins/proxmox/src/frontend/stats/` rather than shared with core's
+  `src/ui/lib/` originals. `useConnectionRetry` (the third duplicate B5 left
+  here) is resolved: **B6** promoted it into `@termix/plugin-sdk/frontend`
+  once file-manager became its fourth caller (after proxmox, docker,
+  host-metrics, remote-desktop) and switched proxmox's own copy over too.
+  host-metrics's own conversion needs `runAdaptivePolling` for its stats tab,
+  so promote it into `@termix/plugin-sdk/frontend` (and `cn` into
+  `@termix/plugin-sdk/ui`) the next time either is touched. Owner: D1, or
+  host-metrics's Phase B step if it lands first.
 - **B5 (proxmox):** `runDueProxmoxAutoSyncs` in
   `plugins/proxmox/src/backend/routes.ts` still reaches
   `createCurrentPluginSettingsRepository`/`createCurrentHostRepository` by
@@ -40,3 +42,41 @@ it's done.
   bulk read today. A `ctx.settings.listHostsWithKey` or similar SDK addition
   would close this, if a second plugin's background scan ever needs the same
   shape. Owner: D1.
+- **B6 (file-manager):** `plugins/file-manager/src/frontend/components/PdfPreview.tsx`
+  runs pdfjs without a worker (main-thread parsing) because `termix-plugin
+build`'s esbuild step has no static-asset-copy pipeline the way core's Vite
+  build resolves a `?url` import to a hashed `/assets/` file. Fine for the
+  small files this preview usually opens; restoring a real worker needs the
+  CLI (`packages/plugin-sdk/cli/commands/build.mjs`) to gain a way to emit an
+  extra file into `dist/` and have the frontend reference it by its served
+  `/plugin-assets/<id>/` path. Owner: D1, or whichever step first needs a
+  worker or other static asset from a plugin bundle.
+- **B6 (file-manager):** `transfer-tuning.ts`'s adaptive-tuning profile still
+  persists to a JSON file under `DATA_DIR` rather than `ctx.kv`, and
+  `HostFilesTab.tsx`'s `t()` calls plus the manifest's `contributes.settings.host`
+  `labelKey`s deliberately point at two different key paths (`hosts.*` and
+  `settings.host.*`) for the same three fields, both carrying the same English
+  text - a minor duplication from keeping the host editor's exact existing
+  section verbatim (`registerHostEditorSection`) instead of switching it to
+  the schema-driven settings form. Neither blocks anything; flagging for
+  whoever next touches this plugin's settings UI.
+- **B6 (file-manager):** `TabContext.tsx`'s `computeUniqueTitle` compares
+  `tabType === "file_manager"` (an activity-log type string, not a tab type -
+  the real tab type has always been `"files"`), so that branch has never
+  matched and silently falls through to the terminal title. Pre-existing,
+  unrelated to the conversion; noted rather than fixed per the lean-mode
+  rules. Owner: whoever next touches tab title logic.
+- **B6 (file-manager):** `enable_file_manager`, `default_path` and
+  `scp_legacy` are still live `ssh_data` columns; only the copy-into-plugin-
+  settings migration shipped (`file-manager-settings-migration.ts`). Every
+  core read site the earlier exploration found (`host.ts`,
+  `host-normalizers.ts`, `host-bulk-routes.ts`, `credentials.ts`,
+  `host-internal-routes.ts`, `database.ts`'s encrypt/decrypt round trip,
+  `plugins/host-view.ts`, `ctx-hosts.ts`, plus the frontend's
+  `HostEditorData.ts`/`HostManagerData.ts`/`SidebarTree.tsx`/quick-connect
+  mapping) still reads the column directly rather than
+  `ctx.settings.getHost`. Switching every one of those and then dropping the
+  column in lockstep (`schema.ts`, `db/index.ts`, a drizzle migration per
+  dialect, `schema:generate`) is real, separate work this step didn't
+  attempt, since none of those reads block the plugin conversion itself.
+  Owner: a dedicated follow-up step, or D0.