Find text in terminal scrollback (#4650)

* feat(app): add pane Find to file source

* fix(app): float the pane Find widget and tighten its chrome

Find pushed the first lines of the file down, ran 480px wide with 32px
ghost buttons, and let the replacement input start left of the query
input. Float the CodeMirror top panel out of flow so the widget overlays
the top right of the pane, move the disclosure toggle into a gutter that
spans both rows so the two fields share a leading rail, put the match
count inside the query field, and drop the icon controls to the shared
pane-toolbar chrome the file bar above already uses.

* fix(app): keep the active match visible and drop the Find button

The floating widget covered the active match whenever the match sat under
it and the document was too short to scroll clear. CodeMirror's own panel
scroll margin cannot reveal a first line, so the file integration now owns
placement: the widget renders as an overlay beside the editor, the model
measures it against the active match, and flips it to the opposite corner
only when the current corner collides. Hysteresis keeps navigation from
bouncing the widget between corners.

Also removes the standalone Find button shown while Find is closed, per
user direction. Cmd/Ctrl+F is the entry point.

* fix(app): stop the Find placeholder from hiding Go to line

Hiding `.cm-panels` suppressed every CodeMirror panel in the file editor,
including the Go to line dialog that Mod-Alt-g opens through the same
search keymap. Hide only the inert Find placeholder panel instead, by its
own class, and leave the shared panel container alone.

* feat(app): find text in terminal scrollback

* test(app): account for terminal write completion before barriers

* fix(terminal): only Cmd+F opens Find on macOS; Ctrl+F reaches the shell

* test(app): exercise terminal find shortcuts against real ptys

* test(app): wait for visible vim lines before terminal page down

* test(app): account for vim page overlap in terminal shortcut journey

docs/terminal-performance.md

@@ -26,6 +26,7 @@ Terminal frames share the daemon main event loop with all agent traffic. The `ev
 - **Snapshot catch-up is backpressure-gated.** A stream falls back to a full snapshot only when `outputBytesSinceSnapshot > MAX_TERMINAL_OUTPUT_FRAME_BYTES` (256KB) **and** the client transport reports `bufferedAmount > MAX_CLIENT_BUFFERED_BYTES` (4MB). A client that keeps draining streams continuously, no matter how much output is produced. Before this gate existed, every 256KB of build output dropped a frame and forced a full JSON cell-grid snapshot (~200k objects across IPC) — the historical source of spiky lag and GC hitches.
 - **Plugin daemon sessions report IPC queue bytes.** Their virtual socket increments `bufferedAmount` before `process.send` and decrements it only in the send callback. Text and binary frames share that ordered queue, so the normal snapshot catch-up and physical high-water gates remain valid for server-side plugin SDK traffic.
 - **Client output writes are not serialized per frame.** The emulator runtime drains contiguous plain writes straight into xterm (which buffers internally). Only barrier ops (`clear`, `snapshot`, `suppressInput` writes) wait — behind a zero-length sentinel write — so resets can't interleave with in-flight output.
+- **Find preserves the inspected xterm viewport, including at the live bottom.** Keep its output anchor inside the existing batched write path. Serializing output to preserve a search result would add terminal latency.
 - **Retained terminal tabs in the focused workspace keep their streams.** Hidden mounted terminals continue applying output, so switching tabs does not resubscribe or request a fresh snapshot. The retained-panel LRU bounds the number of live streams; terminals in an unfocused workspace detach.
 - **Terminal size has one daemon-owned claimant.** Focus and direct interaction send a `claim`; later geometry changes from that connection send `update`. A claim transfers ownership even when the dimensions are unchanged, while an update from any other connection is ignored. This lets an owning pane follow splits and keyboard insets without allowing an idle phone or browser to steal the PTY size.