feat(planner): add factory supply priorities

[ApocDev]

Summary

• add block-level Preferred, Normal, and Fallback supply priorities
• support arbitrary numeric tiers and advanced per-export overrides
• allocate shared factory demand through strict priority tiers
• cap incidental/byproduct supply at its already-available rate so priority never scales its source
• report chosen suppliers and allocated rates in Factory What-if
• simplify the block help drawer and document priority behavior
• refresh built-machine bridge state automatically after relevant in-game changes

Verification

• vp check
• factory priority/re-balance unit tests: 14 passed
• app suite: 730 passed; the UDP heartbeat test timed out in the parallel run but passed 6/6 in isolation
• supply-priority mutating E2E: 1 passed
• re-balance mutating E2E: 2 passed
• responsive What-if matrix: 4 passed

Closes #140