scratch: the scratchpad is the inbox, with ways out and a search

A note now leaves the scratchpad by becoming something else: `K` keeps it
as a document, as before; `C` makes it a card where `:card` would put one,
the first line its title; `A` opens `:append` with the document on screen
filled in, Tab completing any other title, and puts the note at its end.

`/api/capture` takes `to: "note"` and `to: "document"` (named as a link
names it), and `note`, the scratch note the text came from, dropped once
the text has landed. Appending keeps the revision before it and indexes
links and media, as a save does.

Migration 0028 adds `scratch_fts`; `GET /api/scratch?q=` searches it, and
`/` lists note hits under "notes" after the cards, Enter lowering the
drawer at the note.

The `c` capture line cycles its target with Tab: a card, a note, or a
timed line in today's entry, which `:today <text>` now writes.

migrations/0028_scratch_fts.sql

@@ -0,0 +1,18 @@
+-- The scratchpad is where things are written down before it is clear where
+-- they belong, which makes it the first place to look for something half
+-- remembered. Search finds a note the way it finds a document or a card.
+CREATE VIRTUAL TABLE scratch_fts USING fts5 (body, tokenize = 'unicode61');
+
+CREATE TRIGGER scratch_ai AFTER INSERT ON scratch_notes BEGIN
+    INSERT INTO scratch_fts (rowid, body) VALUES (new.id, new.body);
+END;
+CREATE TRIGGER scratch_ad AFTER DELETE ON scratch_notes BEGIN
+    DELETE FROM scratch_fts WHERE rowid = old.id;
+END;
+CREATE TRIGGER scratch_au AFTER UPDATE OF body ON scratch_notes BEGIN
+    DELETE FROM scratch_fts WHERE rowid = old.id;
+    INSERT INTO scratch_fts (rowid, body) VALUES (new.id, new.body);
+END;
+
+-- The notes written before the triggers existed.
+INSERT INTO scratch_fts (rowid, body) SELECT id, body FROM scratch_notes;