delete the AGENTS.md injection; --dir was always the real anchor

The sidecar seeded an AGENTS.md into the serve's project root telling the agent to read its working
directory from the "Working directory for this session" line in its system prompt. The run path sends no
system prompt, so there was no such line and the instruction had been inert since turns moved off the
serve to `opencode run --dir`.

What it was standing in for, `--dir` does properly — tested rather than assumed
(docs/opencode-phase0-review.md): `--dir` anchors the agent's own file operations, not just the process
cwd, and the anchor survives a multi-step turn with a write in the middle. Nothing replaces it.

The generated file is removed from disk too, not only from the code that wrote it; leaving it would have
kept feeding standing instructions to every session while looking, in the source, as though it were gone.

Also corrects the claim that all OpenCode sessions live in one server's project. True when turns
inherited the serve's directory, false now: one serve lists 7 sessions across several directories, which
is why the cwd filter has to read `directory` rather than assume a single one.

docs/opencode-phase0-review.md, item 2 — Phase 1.

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

src/servers/api/chat/opencode-sessions.ts

@@ -4,9 +4,14 @@ import { getConnection } from './opencode/client';
 import { logger } from './logger';
 
 // The OpenCode analog of claude-sessions.ts. OpenCode's own store is the source of truth, read via the
-// fixed pm2-managed server's HTTP API (never the DB directly). All OpenCode /chat sessions live in that
-// one server's project, so listing is just GET /session. Returns the same shapes as the Claude reader,
-// tagged harness:'opencode', so chat.ts can merge both harnesses transparently.
+// fixed pm2-managed server's HTTP API (never the DB directly). Returns the same shapes as the Claude
+// reader, tagged harness:'opencode', so chat.ts can merge both harnesses transparently.
+//
+// Sessions do NOT all live in one project. That claim was true when turns went through the serve and
+// inherited its directory; turns are now `opencode run --dir <cwd>` subprocesses, so each session
+// records the directory it ran in and one serve happily lists sessions across many. Verified: a single
+// serve returned 7 sessions spread over several directories, which is also why the cwd filter has to
+// read `directory` rather than assume.
 
 /**
  * List OpenCode sessions for a working directory, so each context (/chat pwd, email account, project)