feat(turd): show what each choice changes + recipe-comparison diffs

[ApocDev]

Why

The assistant and the TURD page only understood branches that replace a recipe (the turd_replacements table), so branches that instead unlock a brand-new recipe were invisible. Asked "which Moondrop TURD is best?", the assistant confidently reported a single choice — the master actually has three (Copper addition, Moon light, Carbon capture). The /turd page had the same blind spot and showed each choice as an opaque "N recipes" count.

What

Assistant / data

• New turdChoices tool + recipeInfo.turd enrichment walk the tech-prerequisite graph, so the agent sees every branch of a master: its description, the recipes it swaps (old→new) or newly unlocks, and its modules. Prompt updated to consult it and never assume a single choice.
• Import tech descriptions (new technologies.description column + migration).

/turd page

• Each choice now lists its concrete recipe changes (old→new swaps, + new unlocks) with icons and the master/branch descriptions, instead of a bare count.
• Effect pills are color-coded (speed / productivity / energy) with a tooltip clarifying they act on the affected buildings.

Recipe-comparison hover (reusable RecipeDiff, also ready for Py recipe tiers)

• In/out diff with conventional add/remove/change coloring, colored time (faster/slower), and base /s throughput with % change.
• A choice's module is applied to a swapped recipe's rate only when it runs in the affected building — skipped for building-construction recipes (a recipe that builds a machine gets no module bonus). Productivity skips ignored_by_productivity outputs (barrels/catalysts); speed scales all outputs.

Also

• fix(db): the schema change surfaced a latent issue — makeTestDb built tables by pushing schema.ts while production applies migrations, so the first incremental ALTER collided. Test DBs now provision through the real migration path.
• fix(assistant): sending with no OpenRouter key returned a 500 the UI swallowed (the conversation died silently). Now an up-front banner (linking to Settings) shows when no key is set, and send errors render inline.

Verify

• vp check clean; vp test 170 passing.
• Imported the real dump and confirmed moondrop-upgrade's three branches + descriptions; verified live: the /turd detail, recipe-diff tooltips (incl. the productivity-only-where-it-applies and barrel-exclusion behavior), and the no-key banner.

Docs updated (README.md, docs/ai-assistant.md).