Bind requests to the invoking workspace; persist server ownership (#29)

[TheRealDinghyDog]

Fixes #29 (review finding H-04).

Problem

• The client never sent the directory query parameter, so against an external server (OPENCODE_COMPANION_SERVER_URL) every project-scoped request — session create/list/resume and the /event subscription — resolved against the server process's launch directory, not the invoking repo. A review could inspect, and a write task could edit, the wrong repository. (Verified live: a session created without the query inherits the server's cwd; with the query it scopes to the given path, and listing filters by it.)
• Job records persisted serverUrl but not ownership. Cancel recomputed serverExternal by comparing the recorded URL with the current process's environment — a cancel process without the job-start env var concluded "not external" and sent /global/dispose to a user-managed server.

Fix

• OpencodeServerClient takes a directory option and appends the canonical (realpath) workspace directory to every non-/global/ route — all client routes accept it per the pinned 1.17.15 OpenAPI document. /global/health and /global/dispose stay unscoped.
• All client construction sites (turns, auth status, aborts, cancel) pass the invoking workspace.
• getSessionRuntimeStatus now distinguishes env-configured (external) from persisted plugin-owned servers; background jobs persist serverExternal alongside serverUrl at job start, and runServerTurn progress events carry it so foreground job records get it too.
• interruptServerTurn accepts the persisted flag and no longer infers ownership from the environment. Cancel teardown runs only when the job explicitly recorded plugin ownership (serverExternal === false); a recorded URL with unknown ownership (legacy records) fails safe and leaves the server running.

Tests

• Two workspaces sharing one external fixture server: each gets a session scoped to its own repo, and both event subscriptions carry the right workspace (fixture now honors and records the directory query).
• The review's exact cancel scenario: a job started with an external server, cancelled from an environment without the env var — the session is aborted, the job is cancelled, and the server stays alive (the fixture exits on dispose, so any regression fails the health assertion).
• Client unit test: project routes carry directory, /global/* never does.
• Live check against real OpenCode 1.17.15: POST /session?directory=X and scoped listing behave exactly as coded.
• npm test: 92 passed, 0 failed, 0 skipped.

Server-PID identity verification on teardown remains #31.

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