Add cost-aware desk launch profiles

[jennyf19]

Summary

• keep the existing Agency-aware desk launcher and add repo / connected launch profiles
• make repo the cost-aware default while retaining a connected escape hatch
• dynamically discover and disable enabled plugin-scoped MCPs instead of hardcoding any environment's server names
• pass the verified Workshop root with --add-dir so sibling desks remain readable
• add pure launch-profile tests, CI coverage, and app/extension documentation

Why

A matched end-to-end Workshop workflow (own journal read, cross-desk artifact read, signal write, journal update, deterministic validation) produced equivalent outcomes across tool profiles.

On a tool-heavy environment, the interaction-safe MCP-disabled profile versus the full loadout measured:

• 66.28% less input
• 62.98% less AIU
• 82.87% fewer tool-definition tokens
• 53.58% lower wall-clock

The change discovers plugin MCPs at runtime, so external plain-Copilot users with no ambient plugin MCPs retain effectively the same launch, while internal Agency users avoid carrying unrelated default/plugin MCPs into every topic desk.

Safety and compatibility

• connected profile preserves today's configured tool surface
• discovery failure fails open to connected behavior
• Agency remains preferred when installed; explicit unavailable engine selections fail closed
• executable/helper paths are canonicalized outside the Workshop
• MCP names are validated before becoming arguments
• Windows shell fallback rejects metacharacter-bearing arguments
• cross-desk access is limited to the already verified Workshop root

Validation

• node --test .github/extensions/signals-dashboard/launch-profile.test.mjs
• node --check .github/extensions/signals-dashboard/extension.mjs
• git diff --check
• repeated cold code review found no remaining high-confidence issues