feat: share.keyRules, how long and varied a share key must be

Sharing refuses a key shorter than minLength characters (default 32,
never under 16) or of fewer than minClasses kinds of lowercase,
uppercase, digits and symbols (default 2, so random hex passes),
saying so without showing it. Opening doesn't check.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/ui/app/app.go

@@ -24,6 +24,7 @@ import (
 	"git.kebcloud.no/keb/lazysecrets/internal/commands"
 	"git.kebcloud.no/keb/lazysecrets/internal/provider"
 	"git.kebcloud.no/keb/lazysecrets/internal/ref"
+	"git.kebcloud.no/keb/lazysecrets/internal/share"
 	"git.kebcloud.no/keb/lazysecrets/internal/store"
 	"git.kebcloud.no/keb/lazysecrets/internal/ui/icons"
 	"git.kebcloud.no/keb/lazysecrets/internal/ui/keys"
@@ -84,6 +85,8 @@ type Options struct {
 	// ShareKey is the config's share.key: the secret that encrypts shared
 	// env files, for repos whose .lazysecrets.yaml names none.
 	ShareKey string
+	// ShareRules are what a key's value must be to share with it.
+	ShareRules share.Rules
 	// Dir is the folder lazysecrets runs in: it goes back to where it was
 	// left there, unless it was started on a link. "" doesn't.
 	Dir string
@@ -273,7 +276,8 @@ type Model struct {
 	linked     []provider.Container // vaults opened from links, this session
 	open       *ref.Ref             // reference to open at startup
 
-	shareKey string // the config's share.key
+	shareKey   string      // the config's share.key
+	shareRules share.Rules // and share.keyRules
 
 	// A lazysecrets:// link found on the clipboard, offered in the footer.
 	dismissedLink string // the last link offered: not offered again
@@ -460,7 +464,7 @@ func New(providers []provider.Provider, opts Options) Model {
 	m.spinning = true
 
 	m.cachePath, m.placeDir, m.sourcesAt = opts.CacheFile, opts.Dir, map[string]time.Time{}
-	m.shareKey = opts.ShareKey
+	m.shareKey, m.shareRules = opts.ShareKey, opts.ShareRules
 	m.configFiles, m.statePath, m.changelog = opts.ConfigFiles, opts.StatePath, changelogFields(opts.Changelog)
 	if m.cachePath != "" {
 		m.loadCacheFile()