fix(doctor): dynamic latest_version from origin/main; release v3.15.1 (#92)

v3.15.0 doctor used a hard-coded `latest = "v3.14.0"` fallback, causing
any v3.15.0+ install to report kind=upgrade against a stale value.
`ocp update` would then attempt `git checkout v3.14.0` — a downgrade.

Doctor now fetches `git -C ~/ocp show origin/main:package.json` to
determine the actual latest. On failure (offline, fresh clone, no
remote), falls back to currentVersion so kind=noop instead of
recommending a downgrade.

Regression test added: doctor with unreachable ocpDir falls back to
currentVersion as latest (not the old hardcoded v3.14.0).

Caught during v3.15.0 post-deploy verification on home-mac: ./ocp
doctor reported `kind=upgrade` immediately after v3.15.0 install,
which would have been a critical user-facing bug.

No cli.js citation needed: this is OCP-internal doctor logic with
no corresponding cli.js operation.

Co-authored-by: dtzp555 <dtzp555@gmail.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "open-claude-proxy",
-  "version": "3.15.0",
+  "version": "3.15.1",
   "description": "OCP (Open Claude Proxy) — use your Claude Pro/Max subscription as an OpenAI-compatible API for any IDE. Works with Cline, OpenCode, Aider, Continue.dev, OpenClaw, and more.",
   "type": "module",
   "bin": {