Phase 0: Implement shared/profile-schema.ts (Zod)

[ericmmartin]

Goal

Define and validate the .conductor/profile.yml schema in one place, used by both the orchestrator (Phase 2 TS) and the plugin (Phase 0+ bash).

Acceptance criteria

• packages/shared/src/profile-schema.ts exports a Zod schema for the full profile (see docs/profile-reference.md)
• All sensitive fields are *_env only (validator rejects literal channel_id, tenant_id, etc.)
• loadProfile(path: string): Profile reads + validates + returns typed object
• Unit tests covering: valid profile loads cleanly, invalid profile (missing required field) fails with a clear error, profile with a literal sensitive value fails with a pointer to the offending field

Notes

This is the source-of-truth schema. The shell lib/profile.sh reader is a parallel implementation for yq-based access; both must stay consistent with what this Zod schema accepts.

Dependencies: #1

semver: minor