Extract project config application

[sabino]

Summary

• move project model path config and seed docs application from src/project.zig into src/project/config.zig
• keep src/project.zig as the orchestration facade via module aliases
• add native Zig coverage for config path matching, depth precedence, package restriction, inline materialization precedence, and seed docs targeting
• update PLAN.md ownership notes for config application

Validation

• zig fmt --check src/project.zig src/project/config.zig
• git diff --check
• changed-file private/secret/path scan: no matches
• timeout 180s zig test src/project/config.zig --cache-dir /tmp/dxt-zig-cache --global-cache-dir /tmp/dxt-zig-global-cache (16 passed)
• timeout 180s zig build --cache-dir /tmp/dxt-zig-cache --global-cache-dir /tmp/dxt-zig-global-cache
• timeout 240s zig build test --cache-dir /tmp/dxt-zig-cache --global-cache-dir /tmp/dxt-zig-global-cache
• timeout 240s zig build -Doptimize=ReleaseSafe --cache-dir /tmp/dxt-zig-cache --global-cache-dir /tmp/dxt-zig-global-cache
• python scripts/check_runtime_boundary.py && python scripts/check_public_safety.py
• pytest -q tests/test_cli.py (48 passed)
• pytest -q (52 passed)

Agent review

• subagent explorer recommended this as the next smallest M1A extraction
• codex exec rejected the typed-sort alternative as a worse module boundary
• codex exec diff review: No blocking findings.