send images to opencode, which never needed the fork

B4 properly. The composer gate was the honest stopgap; this is the fix. opencode run takes
attachments with --file, so images work on the subprocess path we already use — the parity
doc had them down as phase 4, behind the serve migration, and they were not.

The bug was one omission: handleOpenCodeChat`s msg type had no images field, so the browser
sent them, the bubble rendered them, and they stopped at that signature. Nothing reported a
loss anywhere.

Attachments are paths, not inline data, so the sidecar spills each image to a temp file for
the length of the turn and removes it in settle — the same place every other per-turn
resource is released, so a killed or superseded turn cleans up too.

The load-bearing detail is `--` before the prompt: --file is an array option, so without the
separator the prompt is eaten as another filename and the turn dies with "File not found:"
followed by the entire message. Confirmed against the binary, and pinned by a test that
records argv from a stub.

list-models now reports each model own capability instead of a hardcoded false — opencode
publishes capabilities.input.image per model and nothing had ever read it. Defaults to false,
so a model that does not declare it keeps the affordance hidden.

Verified end to end: a red png sent over the chat socket to opencode/claude-sonnet-4-6 came
back "Red".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/sidecar/protocol.ts

@@ -197,6 +197,14 @@ export type OpenCodeRunParams = {
   cwd?: string; // passed to `opencode run --dir` — hard-re-anchors tools to this directory
   model?: string; // `providerID/modelID` (e.g. opencode/claude-haiku-4-5); passed to --model verbatim
   resumeSessionId?: string; // OpenCode `ses_…` id to continue (`--session`)
+  /**
+   * Images for this turn, base64 as the browser sent them.
+   *
+   * `opencode run` takes attachments as PATHS (`-f`), not inline data, so the sidecar writes each one to
+   * a temp file and deletes it when the turn ends. They travel as data because that is what crosses the
+   * websocket from the browser, and because officer and the sidecar are not guaranteed to share a disk.
+   */
+  images?: PromptImage[];
   durable?: boolean; // commit turn output to chat_session_events (default true) — see ClaudeSpawnStreamingParams
 };