feat: keep what was loaded between runs, and start where you left off (#2)

Starting lazysecrets again now shows what you had loaded at once, and puts you back where you were.

- **Cache file** `~/.cache/lazysecrets/cache.json` (0600, written atomically): the Sources lists, vaults/scopes, secrets' metadata, Describe results and each list's cursor. **Never values**, and never repos (they're on disk anyway). Loaded on start; lists older than 2 minutes reload in the background as before. Saved every 30s when changed, and on quit.
- **Housekeeping:** entries not loaded for 30 days are dropped, as is everything from accounts no longer signed in (every cache key starts with the account ID). The file has a format version; another version is ignored and replaced. `cache: false` turns it off; `--demo` never uses it.
- **Sources are cached too:** Azure lists subscriptions over the network, so without this the Sources pane would still wait.
- **Go to** searches everything cached straight away, and its background loading now also refreshes lists from an earlier run instead of skipping them.
- **Where you left off:** the state file remembers the selected source, vault or secret per folder (the `--dir` or working directory, 100 most recent folders), and the next start in that folder goes back there quietly (no error if it's gone). Starting on a link skips it.

Docs: `cache:` in config.md, a Cache section, the place in State, and the README Privacy section now mentions the cache file.

Tests: cache round trip with a backend too slow to answer (lists and cursor come from the file), no value in the file, file mode 0600, old and signed-out entries dropped, back where it was left, not for another folder or a link.

This touches `app.go` near PR #1's changes (Model fields, the Update switch), so whichever merges second needs a small conflict fix.

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>
Reviewed-on: #2

internal/store/store.go

@@ -69,6 +69,33 @@ func (s *Store) SetUpdateCheck(c UpdateCheck) error {
 	return s.save(func(d *file) { d.Update = c })
 }
 
+// Place is where lazysecrets was left when it last ran in dir.
+func (s *Store) Place(dir string) (Place, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	p, ok := s.data.Places[dir]
+	return p, ok
+}
+
+// SetPlace remembers where lazysecrets was left in dir.
+func (s *Store) SetPlace(dir string, p Place) error {
+	return s.save(func(d *file) {
+		if d.Places == nil {
+			d.Places = map[string]Place{}
+		}
+		d.Places[dir] = p
+		for len(d.Places) > maxPlaces {
+			oldest := ""
+			for k, v := range d.Places {
+				if oldest == "" || v.At.Before(d.Places[oldest].At) {
+					oldest = k
+				}
+			}
+			delete(d.Places, oldest)
+		}
+	})
+}
+
 // Layout is the user's pane sizing, as offsets from the default layout so
 // it adapts to the terminal size.
 type Layout struct {
@@ -84,8 +111,22 @@ type file struct {
 	Flags map[string]bool `json:"flags,omitempty"`
 	// Update is the last check for a newer release.
 	Update UpdateCheck `json:"update,omitzero"`
+	// Places is where lazysecrets was left, by the folder it ran in.
+	Places map[string]Place `json:"places,omitempty"`
 }
 
+// Place is what was selected when lazysecrets quit: an item's link, and
+// the account and source it was read through.
+type Place struct {
+	Link    string    `json:"link"`
+	Account string    `json:"account"`
+	Source  string    `json:"source"`
+	At      time.Time `json:"at"`
+}
+
+// maxPlaces bounds Places: the folders used most recently are kept.
+const maxPlaces = 100
+
 // UpdateCheck is the last look for a newer release: when, and what the
 // latest was (its tag, changelog and page), so the next start within a
 // day shows it without asking again.