Plugins: stop exposing workspace admin keys in observer links

[willwashburn]

Problem

Relay ships six plugin surfaces that construct https://agentrelay.com/observer?key=<workspace-key>, and several tell the agent to print the real key. The sharpest case is plugins/gemini-relay-extension/commands/status/status.toml, which explicitly says not to print a placeholder.

Affected surfaces:

• plugins/gemini-relay-extension/GEMINI.md
• plugins/gemini-relay-extension/commands/status/status.toml
• plugins/gemini-relay-extension/commands/team/team.toml
• plugins/gemini-relay-extension/commands/fanout/fanout.toml
• plugins/gemini-relay-extension/hooks/session-start.sh
• plugins/codex-relay-skill/SKILL.md

This conflicts with #1379/#1380: the CLI is removing credentials from default output while shipped agent instructions still require printing an owner/admin credential into a transcribed terminal and query string.

Credential contract verified from source

A workspace key does not authenticate the observer realtime stream. Relaycast authenticateRealtimeWs rejects workspace tokens with Observer token required for workspace stream; only an ot_live_* token with stream:read is accepted.

The dashboard currently accepts either rk_live_* or ot_live_* as a login credential. When given a workspace key, its server-side login route validates the key and mints a scoped observer token for the realtime socket. Thus the existing links may function through the dashboard login bridge, but they expose a more powerful workspace administration key than observation requires. Relaycast documentation also says not to embed workspace keys in browser clients or third-party dashboards.

Required outcome

• Remove every instruction and hook that prints or embeds a workspace key in an observer URL.
• Define a safe follow-along flow using a scoped ot_live_* observer token, or omit the link when no observer token has been explicitly provisioned.
• Never place either credential in default transcribed output or a query string without an explicit reveal action and warning; prefer a handoff that avoids URL credential material where supported.
• Add regression coverage that searches shipped plugin assets for workspace-key observer URL construction and imperative instructions to print the real key.
• Update plugin/user documentation so workspace admin keys and observer tokens are not conflated.

Relationship

Follow-up to #1379 and #1380. This is intentionally separate from #1380 so the CLI redaction fix remains reviewable and mergeable on its current scope.