fix(messenger): remove bottom bar flash and scale-down on chat open

[bmc08gt]

Problem

The Send $ button and message input box visibly flashed and resized when entering a chat from the DM feed — the bar loaded a full-width "Send $" button that then crossfaded and scaled down to the pill + input layout.

Root cause

typingConstraints.enabled starts false and only resolves a frame or two after the screen opens, once Room confirms whether the chat has a cash message. The bottom bar's AnimatedContent rendered the default false layout first, then animated the false → true transition — producing the visible flash and full-width→pill resize.

Fix

• Add a resolved flag to TypingConstraints, false until the async typing-enabled query answers at least once.
• Hold the bottom bar invisible but measured (alpha 0) until resolved, then reveal the final layout directly. Because the bar stays measured, SubcomposeLayout still reserves its height and the message list padding never jumps.
• Use a snap transitionSpec (no crossfade / size transform) since the only layout change is the hidden initial resolution. The SendCashButton's own color/label springs still animate the typing interaction.
• Fresh contacts have no chatId, so the observeMessages-driven typing flow never fires. Dispatch TypingEnabled(false) explicitly in that branch so those chats resolve and the bar can't stay hidden forever.

Testing

• ./gradlew :apps:flipcash:features:messenger:compileDebugKotlin — passes.
• Manual: open a chat from the DM feed — the Send $ pill and input box appear together in final form, no flash or scale-down. Open a brand-new contact — the full-width Send $ button still renders correctly.