feat(computer): SSH computer selection + status + workspace default (handoff #2)

Mirrors the cwd/workspace UI for the SSH-computer feature:

- New feature library src/features/computer/:
  - logic/view-model.ts (pure): viewComputer/viewComputerStatus/viewTestResult/
    summarizeComputers/formatHost/knownHostLabel + state->badge for the 4
    ComputerStatusResponse states + SaveComputer/LoadComputerStatus/
    TestComputer/LoadComputers ports. 20 view-model tests.
  - ui/ComputerField.svelte: per-conversation selector (dropdown +
    connection-status badge + Test-connection, polling the selected alias).
  - ui/ComputerSelect.svelte: reusable Local/computers dropdown, shared with
    the workspace default-computer control.
- AppStore: computerId state + refreshComputer (at every focus site, parallel
  to refreshCwd) + setComputer (PUT /conversations/:id/computer, null=clear) +
  global computers catalog (GET /computers on boot, like models) +
  computerStatus(alias) + testComputer(alias). chat.send UNCHANGED (resolved
  server-side like cwd).
- App.svelte: ComputerField in the Model sidebar view next to CwdField; adapted
  ports wrap the store.
- workspaces: setDefaultComputer on WorkspaceHttp+WorkspaceStore
  (PUT /workspaces/:id/default-computer); default-computer selector in
  WorkspaceCard (reuses ComputerSelect); router passes store.computers through.
- Re-mirrored .dispatch/transport-contract.reference.md (Computers section +
  ChatRequest.computerId); updated .dispatch/wire.reference.md (Computer/
  ComputerEntry/defaultComputerId + the provider-retry divergence note from
  handoff #1); GLOSSARY + backend-handoff.md (handoff #2, §2e).

Transparency invariant: the computer is USER-facing only (a tool-execution
target, never part of the model prompt); the agent never sees it.

Verify: 795/795 tests green; biome clean; vite build succeeds; 0 typecheck
errors from the computer feature. (11 pre-existing svelte-check errors remain
from the open §2d provider-retry divergence — backend feature/ssh-support
still lacks TurnProviderRetryEvent; not from this feature.)

1 files changed, 39 insertions, 0 deletions

diff --git a/src/features/computer/ui/ComputerSelect.svelte b/src/features/computer/ui/ComputerSelect.svelte
new file mode 100644
index 0000000..d693140
--- /dev/null
+++ b/src/features/computer/ui/ComputerSelect.svelte
@@ -0,0 +1,39 @@
+<script lang="ts">
+	import type { ComputerEntry } from "@dispatch/wire";
+
+	let {
+		value,
+		computers,
+		disabled = false,
+		onSelect,
+	}: {
+		/** The currently selected computer alias, or null for "Local (none)". */
+		value: string | null;
+		/** Discovered computers from `GET /computers` (read-only). */
+		computers: readonly ComputerEntry[];
+		disabled?: boolean;
+		onSelect: (computerId: string | null) => void;
+	} = $props();
+
+	// A `<select>` value is a string; map "" ↔ null (Local). The chosen option's
+	// value is the alias, with "" meaning "clear / local".
+	const selectValue = $derived(value ?? "");
+
+	function onChange(e: Event) {
+		const v = (e.currentTarget as HTMLSelectElement).value;
+		onSelect(v === "" ? null : v);
+	}
+</script>
+
+<select
+	class="select select-bordered select-sm w-full font-mono text-xs"
+	value={selectValue}
+	disabled={disabled}
+	onchange={onChange}
+	aria-label="Computer"
+>
+	<option value="">Local (none)</option>
+	{#each computers as c (c.alias)}
+		<option value={c.alias}>{c.alias}{c.knownHost ? "" : " · new host"}</option>
+	{/each}
+</select>