feat(queries): make Sent a saved query rather than a fixed button

The user asked whether the default queries could be unified with Sent. The
answer runs the other way: Sent joins the saved queries rather than the saved
queries becoming hardcoded.

Inbox, Unread and Important are complete strings that depend on nothing and can
never go stale, so generating them would buy nothing and would cost the four
things the file just gained: reordering, unpinning, renaming and deleting.
Hardcoding them would also make them undeletable, which is a regression for
anyone who does not want one of them.

Sent is different only in that its query CANNOT be stored: it is composed from
every account's `sent` key, so a stored copy goes stale the moment a folder is
renamed. That is a property of Sent, not of "default queries". Storing the
GENERATOR rather than its output keeps both halves: `"generated": "sent"` still
resolves from the accounts at click time, and the entry is an ordinary row that
can be reordered, renamed, unpinned or removed. The row now follows one rule
instead of carrying one member the user did not own.

Two properties had to travel with the entry. The composed query, resolved
through Config::resolvedQuery() so what lands in the bar is what actually ran;
and FLAT mode, since a sent view lists messages and a threaded one folds every
reply back into the conversation the user sent one message into. The sent
generator implies flat rather than trusting the file to say so, because a
hand-edited row would otherwise produce a threaded sent view.

An unknown generator is reported but the row is KEPT: a later build may know it,
and dropping it here would delete it from the file on the next save, which is
the same data loss the unknown-field handling exists to prevent. A generator
whose accounts configure nothing is skipped entirely, exactly as the hardcoded
button was hidden rather than offering one that finds nothing.

Eight new tests. The four pre-existing Sent tests reach this through migration
and were left alone, which is what proves the migrated path still behaves; the
new ones cover a STORED file, which is the path every launch after the first
takes. Mutations: a generator resolving to nothing fails three, ignoring flat
fails two, and not skipping an empty generator fails one. A rename test guards
the property the change exists for, since anything keyed on the literal name
"Sent" would break it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 24 insertions, 4 deletions

diff --git a/README.md b/README.md
index 81ec7d8..749d89d 100644
--- a/README.md
+++ b/README.md
@@ -223,16 +223,36 @@ queries** menu, which keeps the row usable once you have more than a handful.
 same as choosing that account in the dropdown; leave it out for a query that
 spans every account.
 
+**Sent is an entry like any other**, and the one that carries `generated`
+instead of `query`:
+
+```json
+{ "name": "Sent", "generated": "sent", "pinned": true }
+```
+
+A generated query is composed from your accounts every time you click it,
+rather than stored. That is why Sent has no `query` of its own: it is built
+from every account's `sent` key, so adding an account or correcting a folder
+name updates the button with no edit here. A stored copy of the same string
+would quietly go on naming the old folder.
+
+Being an ordinary entry, it can be reordered, renamed, unpinned or deleted like
+the rest. Renaming it to `Posta inviata` changes only the label. `sent` is the
+only generator today, and it is skipped entirely when no account configures a
+sent folder, rather than offering a button that finds nothing.
+
 The name is what the button says, so `Important` and `Flagged` can run the same
 query and differ only in the label.
 
 **Upgrading from 0.17.0 or earlier.** Saved queries used to live in a
 `[queries]` section of `qtmaildir.conf`. The first launch after upgrading reads
 that section, writes `queries.json` from it, and marks every entry pinned so
-your buttons stay where they were. Your config file is not modified: the old
-`[queries]` section is left exactly as it is, ignored from then on, and you can
-delete it by hand whenever you like. The reason it is not removed for you is
-that rewriting the file would drop your comments and reorder your keys.
+your buttons stay where they were. Sent is added as a `generated` entry at the
+end, where its button already sat, provided an account configures a sent
+folder. Your config file is not modified: the old `[queries]` section is left
+exactly as it is, ignored from then on, and you can delete it by hand whenever
+you like. The reason it is not removed for you is that rewriting the file would
+drop your comments and reorder your keys.
 
 One behaviour changes with the move. Buttons used to appear in alphabetical
 order, because the INI backend returns keys sorted and preserving file order