feat(servers): Phase 3 — Panel Form mode

Autonomous decisions:
- Default panel mode to Form — guided creation is the primary UX now that fields exist
- Env vars stdio-only in form UI — space config http entries do not carry env at sync time
- default_params persisted in JSON entry — mirrors Configure modal field; kept out of schema-validated core fields

Signed-off-by: crimsonsunset <jsangio1@gmail.com>

Author: crimsonsunset