CB-592: the tracked opencode.json must name the worker forge token, not the admin one

Operator's rule, 2026-08-15: only the leader and architects may use GITEA_ACCESS_TOKEN;
everyone else uses WORKER_GITEA_TOKEN.

opencode.json is TRACKED, so it ships in every worker worktree, and it mounted the gitea
MCP with {env:GITEA_ACCESS_TOKEN}. A live probe confirmed that variable actually resolves
inside a member: herdr spawns each pane from its own login-shell environment and layers
the launcher's map on top, so a member sees 108 variables rather than the small explicit
set baseEnv appears to build. That gave an opencode member admin forge TOOLS — enough to
merge its own PR, which both CLAUDE.md and the member contract forbid.

This is the narrow half of the fix: it removes the tooling. The admin token is still
present as a string in every member's environment, which is the real defect and is
tracked as CB-592 (gitea #77) — that fix belongs in the launcher, in one place, not
per-profile in bridged.yaml where a sixth profile would silently reopen it.

.mcp.json keeps GITEA_ACCESS_TOKEN and is correct to: it is skip-worktree, the primary's
own local copy, and the primary is the lead. That is the pattern this change follows —
the shared tracked file grants least privilege, and anything needing more overrides
locally.

opencode.json

@@ -26,7 +26,7 @@
       ],
       "enabled": true,
       "environment": {
-        "GITEA_ACCESS_TOKEN": "{env:GITEA_ACCESS_TOKEN}",
+        "GITEA_ACCESS_TOKEN": "{env:WORKER_GITEA_TOKEN}",
         "GITEA_HOST": "{env:GITEA_HOST}"
       }
     }