[Feat] Make plan mode always on and introduce the Advisor model role with a coding-advisor subagent

[roomote-roomote]

Opened on behalf of Matt Rubens. Follow up by mentioning @openmote, in the web UI, or in Slack.

What changed

• Plan mode is now always on. The PlanMode feature flag has been removed entirely (enum entry, config registry, metadata typing, worker flag evaluation, the ROOMOTE_PLAN_MODE env plumbing, and the harness gating), following the same graduation pattern as PrReviewNotifications. Plan-mode turns now switch onto the read-mostly architect agent whenever the planning workflow skill is active, with no per-deployment toggle.
• The planning model role is now called "Advisor" in the UI. The Settings > Models role label, placeholder, aria labels, validation error, and the public docs (models.mdx, environment-variables.mdx) all use "Advisor model" now. Internal identifiers and the R_PLANNING_MODEL / R_PLANNING_MODEL_REASONING_EFFORT env vars are intentionally unchanged, so existing configuration keeps working and the planning workflow (architect agent) keeps using the same model wiring.
• New advisor subagent for coding tasks. Every generated OpenCode config now registers a visible (non-hidden) advisor subagent, and the parent coding agent gets instructions to consult it when it is stuck: repeated failed attempts, confusing bugs, or uncertain approach/design decisions. The advisor uses the configured Advisor model when one is set, and otherwise defaults to the active coding model running at the advisor reasoning level (which defaults to high, vs. medium for ordinary coding turns). It is read-only (no edit/bash/task) with webfetch allowed, and excludes Slack-posting tools like the other subagents.

A changeset is included since this is user-facing.

How it was tested

• Added two bootstrap tests covering the advisor subagent: one with a dedicated planning/advisor model configured (agent-level model + reasoning options) and one proving the coding-model fallback with the advisor reasoning level applied.
• Updated the harness tests for always-on plan mode (removed the plan-mode-disabled cases), removed the flag-evaluation run-task tests, and updated the feature-flag config and ModelSettingsSection tests for the removed flag and new labels.
• pnpm lint, pnpm check-types, and pnpm --filter @roomote/docs check pass; feature-flags, SDK feature-flag router, worker bootstrap/harness/run-task suites (133 tests), and the affected web test suites all pass.

Screenshots

Checklist

• The PR title follows the repo convention: [Fix], [Feat], [Improve], [Refactor], [Docs], or [Chore] followed by a user-facing description
• This PR is small and scoped to one change
• pnpm lint and pnpm check-types pass locally
• I added tests or included a clear manual validation note above
• I removed secrets, tokens, private keys, and customer data from code, logs, and screenshots
• If this change should appear in the changelog, I ran pnpm changeset

[roomote-roomote]

No new code issues found. See task

Re-reviewed the latest update, which removes the PlanMode feature flag entirely and makes plan mode always-on (the flag is no longer an opt-out). The delta is clean and internally consistent:

• Flag fully removed. FeatureFlag.PlanMode, the plan_mode config entry, MetadataRecord.plan_mode, the mockFeatureFlags entry, and the runTask flag evaluation are all gone. A repo-wide search finds no remaining PlanMode / plan_mode / ROOMOTE_PLAN_MODE code references — only the changeset prose mentions it. @roomote/feature-flags and @roomote/worker both type-check clean.
• Harness gating simplified correctly. isPlanModeEnabled() was removed, and both resolvePromptAgent() and the plan-exit continuation now key only on the active workflow skill. This is safe because resolveWorkflowSkillTransition already scopes queueContinuation to the real plan→implement exit case (inFlight && previousSkill === PLAN_WORKFLOW_SKILL && loadedSkill !== PLAN_WORKFLOW_SKILL), so behavior matches "plan mode always on."
• Advisor subagent unhidden. Dropping hidden: true and the matching "A hidden" wording in the advisor instructions is consistent across config, instruction text, and the bootstrap tests.
• Tests updated in lockstep. The obsolete plan-mode-flag runTask tests and the plan-mode-disabled harness tests were removed, the enabled-path harness test was renamed to the unconditional behavior, and the feature-flag config test for the old default was dropped. The changeset note now accurately describes the flag's full removal.