Initial commit: Kecalek Android client

Complete Android client for encrypted chat platform.
78+ Kotlin files: crypto (X3DH, Double Ratchet, AES-GCM, Ed25519, X25519,
RSA-PSS), network (TCP/TLS, 50 endpoints), Hilt DI, Room+SQLCipher DB,
Jetpack Compose UI with Catppuccin Mocha theme.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

specs/agent-k-reactions-pins-search.md

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+# Agent K: Reactions, Pins, Search, Forward
+
+## Phase: 4 (Feature Completion)
+## Depends on: Agent F (Chat Screen with MessageBubble)
+
+## Context
+These features enhance the chat experience. Reactions use 6 predefined emoji.
+Pins allow highlighting important messages. Search is client-side through cached messages.
+Forward sends messages to other conversations with attribution.
+
+## Task
+Create reaction picker, pin UI, search overlay, forward dialog, and @mention autocomplete.
+
+## Files to Create
+
+### 1. ui/chat/ReactionPicker.kt
+Emoji reaction picker composable:
+- **Layout**: Horizontal row of 6 emoji buttons in a rounded Surface1 card
+- **Emoji**: thumbsup, heart, laugh, surprised, sad, thumbsdown
+- **Display**: Use emoji characters (not images)
+- **Behavior**:
+  - Shown as popup/overlay near the long-pressed message
+  - Tap emoji: add reaction (or remove if already reacted)
+  - Dismiss on outside tap
+- **Animation**: Scale-in animation when appearing
+
+### 2. ui/chat/ReactionBadge.kt
+Reaction display below messages:
+- **Layout**: FlowRow of reaction chips
+- **Each chip**: emoji + count in a small pill shape
+  - Background: Surface1 (or Lavender alpha if user reacted)
+  - Border: Surface2 (or Lavender if user reacted)
+  - Text: emoji (14sp) + count (12sp)
+- **Behavior**: Tap to toggle own reaction
+
+### 3. ui/chat/PinnedMessagesSheet.kt
+Bottom sheet showing pinned messages:
+- **Header**: "Pinned Messages" title + close button
+- **List**: LazyColumn of pinned messages
+  - Each item: sender name + message text preview + pin date
+  - Tap: scroll to message in chat (dismiss sheet)
+- **Empty state**: "No pinned messages"
+
+### 4. ui/chat/SearchOverlay.kt
+Search bar overlay at top of chat screen:
+- **Layout**: Row with:
+  - Search TextField (weight 1f, with search icon)
+  - Match count text ("3 of 12")
+  - Up arrow button (previous result)
+  - Down arrow button (next result)
+  - Close button (X)
+- **Behavior**:
+  - Activated by search icon in top bar
+  - Results update as user types (debounced 300ms)
+  - Current match highlighted differently from other matches
+  - Up/Down cycle through results
+  - Escape or X closes search
+- **Match highlighting in messages**: Yellow background on matching text
+
+### 5. ui/chat/ForwardPickerDialog.kt
+Dialog for selecting forwarding target:
+- **Title**: "Forward to..."
+- **Conversation list**: LazyColumn of all user's conversations
+  - Each item: avatar + conversation name
+  - Tap: forward to that conversation and dismiss
+- **Search field**: Filter conversations by name
+- **Cancel button**
+
+### 6. ui/chat/MentionAutocomplete.kt
+@mention autocomplete popup:
+- **Trigger**: Typing "@" in message input
+- **Layout**: Popup above the text input
+  - LazyColumn of matching member names
+  - Each item: avatar (24dp) + username
+- **Behavior**:
+  - Filters as user types after "@"
+  - Tap: inserts "@username " into text field
+  - Dismiss on escape, backspace past "@", or clicking outside
+- **Styling**: Surface1 background, elevated (shadow)
+
+## Reaction Emoji Mapping
+```
+"thumbsup"    -> 👍
+"heart"       -> ❤️
+"laugh"       -> 😂
+"surprised"   -> 😮
+"sad"         -> 😢
+"thumbsdown"  -> 👎
+```
+
+## Constraints
+- Reaction picker uses emoji characters (Unicode), not custom images
+- Search is debounced (300ms) to avoid excessive computation
+- Forward dialog loads conversation list from local cache
+- @mention autocomplete only shows members of current conversation
+- All animations should be subtle and fast (200-300ms)
+
+## DO NOT
+- Implement actual server calls for reactions/pins
+- Handle message encryption for forwarding
+- Implement full-text search indexing (just LIKE query on cached text)