refactor: apply engine configuration in one place (the MCP binary applies none) #1515

Problem

uteke.toml and env are read and applied three different ways:

• CLI (uteke-cli/src/config.rs, main.rs): ~14 section structs, then set_jaccard_weight, set_dream_config, set_lifecycle_config, set_fallback_settings, set_privacy_config by hand.
• Server (uteke-server/src/main.rs): ServerFileConfig plus its own Option unwrap chains for the same fields.
• MCP (uteke-mcp/src/main.rs): Uteke::open and set_privacy_config only. Recall and dream over MCP run with defaults the CLI does not use on the same store (jaccard weight, dream thresholds, lifecycle, tier, fallback).

The merge and trust policy is already shared (config_layers); the schema and the apply step are not.

Direction

One module owns TOML layering, env precedence and a single apply step that all three binaries consume. Absorbs #1355.

Behaviour impact

MCP results can change (a fix, but observable); mention in the release notes. CLI and HTTP behaviour must stay byte-identical (same defaults per binary where they differ today: server uses RecallConfig::default(), CLI the configured min_score; decide and document).

Acceptance

• The three binaries share one apply step; no per-field copies remain.
• MCP honours [recall], [dream], [lifecycle], [tier], [embed_fallback] (test with a temp uteke.toml).
• Existing config tests pass unchanged or are replaced by tests at the new interface.
• refactor: unify the mirrored config schema structs (CLI Config vs server ServerFileConfig) #1355 closed.

Part of the round-2 deepening epic.