Seed provenance + inventory: source links and seed lots (#50) (#64)

Co-authored-by: Steve Dudenhoeffer <[email protected]>

internal/store/migrations/0007_seed_lots.sql

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+-- Seed provenance and inventory (#50): where "German Red Garlic" came from, and
+-- how much of it is left.
+--
+-- Two modelling calls worth stating, because both look like omissions otherwise:
+--
+--   1. The plant catalog stays FLAT. No species→variety hierarchy. A row in your
+--      catalog just is the thing you plant — "German Red Garlic" is a plant row,
+--      and the built-in "Garlic" is a generic starting point you clone. A
+--      hierarchy buys taxonomy nobody asked for and complicates every join.
+--
+--   2. Inventory belongs to a PURCHASE, not to a variety. You might buy the same
+--      garlic from two vendors in two years at two prices and two germination
+--      rates. Quantity columns on plants would collapse all of that into one
+--      number and lose it, so lots get their own table.
+--
+-- Nothing here is destructive: plants gains two defaulted columns, the built-ins
+-- keep working with empty strings, and plantings gains a nullable link.
+ALTER TABLE plants ADD COLUMN source_url TEXT NOT NULL DEFAULT '';
+ALTER TABLE plants ADD COLUMN vendor     TEXT NOT NULL DEFAULT '';
+
+-- owner_id sits on the LOT rather than being inherited from the plant, because a
+-- lot may reference a built-in plant (you can buy generic Garlic from Johnny's)
+-- while still being nobody's business but yours. Lots are never shared along
+-- with a garden.
+CREATE TABLE seed_lots (
+    id              INTEGER PRIMARY KEY,
+    owner_id        INTEGER NOT NULL REFERENCES users (id)  ON DELETE CASCADE,
+    plant_id        INTEGER NOT NULL REFERENCES plants (id) ON DELETE CASCADE,
+    vendor          TEXT    NOT NULL DEFAULT '',
+    source_url      TEXT    NOT NULL DEFAULT '',
+    sku             TEXT    NOT NULL DEFAULT '',
+    lot_code        TEXT    NOT NULL DEFAULT '',
+    purchased_at    TEXT,                                   -- 'YYYY-MM-DD'
+    packed_for_year INTEGER,
+    quantity        REAL    NOT NULL DEFAULT 0,
+    unit            TEXT    NOT NULL CHECK (unit IN ('seeds','grams','ounces','packets','bulbs','plants')),
+    cost_cents      INTEGER,
+    germination_pct REAL,
+    notes           TEXT    NOT NULL DEFAULT '',
+    version         INTEGER NOT NULL DEFAULT 1,
+    created_at      TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+    updated_at      TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now'))
+);
+
+CREATE INDEX idx_seed_lots_owner ON seed_lots (owner_id);
+CREATE INDEX idx_seed_lots_plant ON seed_lots (plant_id);
+
+-- Which lot a planting came out of. ON DELETE SET NULL rather than CASCADE:
+-- retiring a lot must never destroy planting history — the plants really were in
+-- the ground, whatever happened to the record of the packet.
+ALTER TABLE plantings ADD COLUMN seed_lot_id INTEGER REFERENCES seed_lots (id) ON DELETE SET NULL;
+
+CREATE INDEX idx_plantings_seed_lot ON plantings (seed_lot_id) WHERE seed_lot_id IS NOT NULL;