Providers and hosts: what runs, and where, as independent choices

A session now names a provider (what: driver kind, command, models) and
optionally a host (where: an ssh target). Keeping them independent is
what the real setup needs -- the backend runs where the phone can reach
it, which isn't where the CLI is installed -- and it means any provider
can be sent to any host rather than a machine being baked into one.

The first provider is claude-cli, named for the CLI rather than bare
"claude", which would suggest the credit-billed API. A fresh config is
seeded with it so a new install has something to spawn and a worked
example to edit; echo stays a built-in provider needing no config.

ssh.rs builds the child process either way: locally, or `ssh -T` with
BatchMode and keepalives, every argument single-quoted for the remote
shell (a working directory that tries to close the quote and start a
command is covered by a test), and `exec` so dropping the connection
takes the CLI down instead of orphaning it.

App: the spawn screen reads /providers and /hosts instead of hardcoded
lists, so config changes need no rebuild. Chip rows are FlowRow, fixing
the reported bug where a row of models that didn't fit wrapped *inside*
each chip -- one letter of "haiku" per line -- rather than onto a second
line.

Verified: 29 tests, clippy clean; the same claude-cli provider run once
locally and once over ssh, with the remote one visibly in a different
environment; an unknown host name refused with the configured list; and
the spawn screen on the emulator showing server-driven providers, hosts,
and models that wrap.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw

app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt

@@ -224,7 +224,8 @@ fun SessionScreen(settings: ServerSettings, summary: SessionSummary, onBack: ()
                 Text(summary.title, style = MaterialTheme.typography.titleMedium)
                 Text(
                     listOfNotNull(
-                        summary.kind,
+                        summary.provider,
+                        summary.host?.let { "on $it" },
                         summary.model,
                         if (totalTokens > 0) "$totalTokens tok" else null,
                     ).joinToString(" · "),