refactor(ssh): rebuild Settings → SSH as a host library

The section was a field editor wearing a list's clothes: the widest
column on the page said "Select a profile to edit" and nothing else, the
global security toggles hung underneath whichever host happened to be
open, and port forwards had to be typed as `L bind:port target:port` into
a text area that taught the syntax nowhere and silently dropped any line
it couldn't parse.

The master column now leads with a title and a filter — past a dozen
hosts, finding one is the job — with Add and the `~/.ssh/config` import
demoted to icon affordances beside it. Hosts bucket by group into
collapsible sections; a collapsed header keeps showing how many of its
hosts are connected, and collapsing the group holding the selection hands
the detail pane back to Defaults rather than stranding a selected row
nobody can see. A live query force-expands every group.

`Defaults` is now a pinned row with its own page, so "every host starts
from these and can override one" is something the list's shape says. Each
per-host override names the value it currently inherits instead of
claiming a mechanism exists.

A selected host leads with its own name, address, jump chain and live
status, then Save (disabled with nothing to write) and Connect. Save
leaves the form open — with the list permanently beside it, closing back
to an empty pane read as the selection being thrown away.

Port forwards are one row of inputs per rule, and a rule that can't
connect is flagged in place rather than dropped on save.

With nothing selected the pane offers quick connect and, when
`~/.ssh/config` holds aliases tty7 hasn't linked, an offer to link them.

src/ui/app.rs

@@ -4339,6 +4339,29 @@ impl Tty7App {
             }),
         );
 
+        // Live filter for the SSH section's host list; each keystroke re-renders
+        // the master column so the list narrows as you type.
+        let ssh_filter = cx.new(|cx| InputState::new(window, cx).placeholder("Filter hosts…"));
+        subs.push(
+            cx.subscribe_in(&ssh_filter, window, |_this, _i, ev, _w, cx| {
+                if matches!(ev, InputEvent::Change) {
+                    cx.notify();
+                }
+            }),
+        );
+
+        // The SSH empty state's quick-connect box. Its Connect button enables only
+        // on a parsable target, so each keystroke re-renders the pane.
+        let ssh_quick_connect =
+            cx.new(|cx| InputState::new(window, cx).placeholder("user@host  or  user@host:port"));
+        subs.push(
+            cx.subscribe_in(&ssh_quick_connect, window, |_this, _i, ev, _w, cx| {
+                if matches!(ev, InputEvent::Change) {
+                    cx.notify();
+                }
+            }),
+        );
+
         self.settings = Some(SettingsState {
             focus_handle: focus_handle.clone(),
             section: SettingsSection::Appearance,
@@ -4360,6 +4383,9 @@ impl Tty7App {
             rebinding_note: None,
             ssh_form: None,
             ssh_detail: crate::ui::settings::SshDetail::None,
+            ssh_filter,
+            ssh_collapsed_groups: std::collections::HashSet::new(),
+            ssh_quick_connect,
             agent_hooks_host: crate::ui::host_ops::HostId::LOCAL,
             agent_hooks_states: crate::ui::settings::AgentHooksView::Loading,
             agent_hooks_seq: 0,
@@ -7291,6 +7317,19 @@ mod keybinding_gpui_tests {
     use gpui::{AppContext, Entity, TestAppContext, VisualTestContext};
 
     fn harness(cx: &mut TestAppContext) -> (Entity<Tty7App>, VisualTestContext) {
+        // Every keybinding edit below goes through `update_config`, which ends in
+        // `Config::save()` — a *full* overwrite of `config.json` at whatever path
+        // the config dir resolves to. Unpinned, that is the developer's real
+        // `~/.config/tty7/config.json`, so running these tests silently reset the
+        // user's entire config to `Config::default()` plus the shortcut recorded
+        // here. Pin a scratch dir first, like every other test module that
+        // touches config-dir files (`set_config_dir` is first-call-wins, so this
+        // is a no-op when another test in the same process already pinned one —
+        // also a scratch dir, so the real file stays untouched either way).
+        let dir = std::env::temp_dir().join(format!("tty7-kbtest-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).ok();
+        crate::core::config::set_config_dir(dir);
+
         // The pause-to-commit is a real `smol::Timer` (off the deterministic
         // executor), so waiting on it parks the test thread.
         cx.executor().allow_parking();