feat(alias): add a shared alias dictionary invocable as a bare command

/alias <name> saves a replied message under a name and /insert <name> sends it
back; /aliases lists every name and /unalias deletes one. Every Telegram format
is supported — sticker, photo, GIF, video, video note, audio, voice, document,
plain text — and each is kept as the file_id Telegram already issued, so nothing
is downloaded and an alias survives redeploys. The namespace is global and the
last assignment wins, matching the shared sticker pack; /unalias is open to
anyone for the same reason.

A saved name also works as its own command: /cheer rather than /insert cheer.
This needs two new seams in the module contract. Module.Fallback handles a
/command no module registered, and the dispatcher installs it after every
Command — the bot library returns the first matching handler, so code always
beats a name resolved at runtime, including an alias that shares a command
added in a later build. /alias refuses a name already in the registry for the
same reason, since such an alias would only reach /insert. An unknown command
stays silent: the fallback sees every unrecognised /foo in every chat, so
replying would make typos noisy and would confirm which names exist.

Module.Inline answers inline-mode queries — "@botname <prefix>" from any chat,
filtered by prefix and capped at Telegram's 50 results. Each result is a cached
inline type carrying the stored file_id, so the picker renders real previews
without an upload. Video notes are omitted because Telegram defines no
InlineQueryResultCachedVideoNote and substituting a plain video would change
what was saved. Inline mode must be enabled in BotFather before Telegram
delivers these updates.

Both slots are single-occupancy with conflict detection at Build. Auth.Permits
learns the inline sender so a gated inline handler would not deny everyone.
Build's command indexing and slot claiming move into addCommands/addSingletons,
keeping it under the project's cyclomatic cap.

Also restores the sticker module: /addsticker moves back out of util, which has
no store, into internal/modules/sticker as its only command.

cmd/server/command_menu_test.go

@@ -73,6 +73,10 @@ func TestCommandDiscovery_AllPublicCommandsHaveSafeMetadata(t *testing.T) {
 		"monkeyd_tags":         "<url>",
 		"random":               "<option,...>",
 		"addsticker":           "[emoji...]",
+		"alias":                "<name>",
+		"aliases":              "",
+		"unalias":              "<name>",
+		"insert":               "<name>",
 		"stats":                "[users | user <username> | cmd <command_name>]",
 		"stock_events":         "<ticker> [days]",
 		"stock_info":           "<ticker>",