refactor(orchestrate): prefix Slack env vars with ORCHESTRATE_

[JonnyPower]

Summary

SLACK_BOT_TOKEN and SLACK_CHANNEL_ID are generic enough that orchestrate could pick up an unrelated tool's Slack app from a shared environment, which matters most on cloud agents where secrets are injected per repo. They are now ORCHESTRATE_SLACK_BOT_TOKEN and ORCHESTRATE_SLACK_CHANNEL_ID, matching the ORCHESTRATE_ prefix the skill's other settings already use (ORCHESTRATE_MODEL_CATALOG, ORCHESTRATE_TOOL_CALL_IDLE_MS, ORCHESTRATE_OPERATOR).

Before	After
SLACK_BOT_TOKEN	ORCHESTRATE_SLACK_BOT_TOKEN
SLACK_CHANNEL_ID	ORCHESTRATE_SLACK_CHANNEL_ID

Breaking change, deliberately not softened

The old names are not read as a fallback. Honoring them would defeat the isolation this is for: if a teammate's environment sets SLACK_BOT_TOKEN for something else, orchestrate would still post with it.

The risk of a hard rename is that an existing setup goes quiet with no explanation, since an unset token just disables Slack. So a token found only under the old name prints a rename notice instead of the generic disabled line:

[orchestrate] SLACK_BOT_TOKEN is no longer read; rename it to ORCHESTRATE_SLACK_BOT_TOKEN. Slack visibility disabled

Anyone upgrading sees exactly what to change on the next run.

Implementation

Both names now live in constants (SLACK_TOKEN_ENV in adapters/slack/client.ts, SLACK_CHANNEL_ENV in cli/util.ts) rather than string literals spread across six files, and the two places that hand-rolled process.env.SLACK_BOT_TOKEN truthiness checks go through a shared slackTokenConfigured(). User-facing messages, CLI --slack-channel help text, and the plan.slackChannel schema description are updated to the new names, with plan.schema.json regenerated.

Test plan

• bun test (228 pass), including a new slack-env-rename.test.ts covering the prefixed variable enabling Slack, neither variable set, the legacy-only rename notice, and the prefixed one winning when both are set
• bun run check (biome + tsc)
• CLI smoke: with the new token and no channel, kickoff bails naming both new variables; with only the legacy token, Slack is treated as unconfigured and the channel gate does not fire
• Live run: confirm a real kickoff still threads into Slack under the new names