Grow journal: time-stamped notes on gardens, beds and plantings (#52)

"Take notes through the season on each bed and plant." There is already
free-text notes on gardens, objects and plants, but it is a single mutable
field: writing "powdery mildew on the west bed" overwrites what you wrote in
June. The distinction worth keeping is that notes says what this thing IS, while
a journal entry says what HAPPENED, and when. Both stay.

garden_id is NOT NULL even when an entry is about a bed or a single plop, and
that is the whole trick: permission checks reuse requireGardenRole unchanged and
no second ACL path is invented. object_id/planting_id narrow the target; the
garden always anchors it. Because the garden anchors permission, the target is
checked to actually live in that garden — otherwise a valid object id from
someone else's garden would be storable here and then leak through the list
read. A plop-level entry that also names an object must name the right one, or
the two filters would disagree about what an entry is about.

observed_at is distinct from created_at: you write up Saturday's observations on
Sunday, and Saturday is the date that matters. Listing orders by observation,
newest first, with id breaking ties inside a day.

Roles follow the existing shape. Editors write, viewers read, strangers get
ErrNotFound. An author may edit their own entries; the garden owner may DELETE
any entry in their garden but may not edit one — rewriting somebody else's
observation under their name is a different act from removing it.

Deliberately not wired into the revision history, per the decision on #52:
entries are already append-shaped and individually versioned, and undoing a note
is just deleting it. There's a test asserting journal writes produce no change
sets, so that decision can't quietly reverse itself later.

Closes #52

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

internal/store/migrations/0008_journal.sql

@@ -0,0 +1,33 @@
+-- Grow journal (#52): time-stamped notes on gardens, beds and plantings.
+--
+-- There is already free-text `notes` on gardens, objects and plants, but it is a
+-- single mutable field: writing "powdery mildew on the west bed" overwrites what
+-- you wrote in June. The distinction worth keeping is that `notes` is WHAT THIS
+-- THING IS, while a journal entry is WHAT HAPPENED, AND WHEN. Both stay.
+--
+-- garden_id is NOT NULL even when the entry is about a bed or a single plop, and
+-- that is the whole trick: permission checks reuse requireGardenRole unchanged
+-- and no new ACL path is invented. object_id/planting_id narrow the target; the
+-- garden always anchors it.
+--
+-- observed_at is deliberately distinct from created_at — you write up Saturday's
+-- observations on Sunday, and the date that matters is Saturday's.
+CREATE TABLE journal_entries (
+    id          INTEGER PRIMARY KEY,
+    garden_id   INTEGER NOT NULL REFERENCES gardens (id)        ON DELETE CASCADE,
+    object_id   INTEGER          REFERENCES garden_objects (id) ON DELETE CASCADE,
+    planting_id INTEGER          REFERENCES plantings (id)      ON DELETE CASCADE,
+    author_id   INTEGER NOT NULL REFERENCES users (id)          ON DELETE CASCADE,
+    body        TEXT    NOT NULL,
+    observed_at TEXT    NOT NULL,                               -- 'YYYY-MM-DD'
+    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'))
+);
+
+-- The journal's only list query: one garden, most recently observed first.
+CREATE INDEX idx_journal_garden ON journal_entries (garden_id, observed_at DESC);
+
+-- Narrowing to one bed or one plop.
+CREATE INDEX idx_journal_object ON journal_entries (object_id) WHERE object_id IS NOT NULL;
+CREATE INDEX idx_journal_planting ON journal_entries (planting_id) WHERE planting_id IS NOT NULL;