Add keybinding / @file for fuzzy file search in chat

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

macOS 15.3.0 (24D60)

### Expected behaviour

Users could use a keyboard shortcut or type "@file" in the chat to trigger a fuzzy search interface that allows quickly finding and adding files to the conversation. This would make it easier to reference local files without having to type full paths.

### Actual behaviour

Currently, users need to manually type or paste full file paths when they want to reference files in the chat. There's no quick way to search for and select files from the local filesystem.

### Steps to reproduce

_No response_

### Environment

```yaml

[q-details]
version = "1.7.3"
hash = "3d0e57a070c7819e27b92f8a314b1ae5bbe9a7db"
date = "2025-04-09T19:28:20.909702Z (7d ago)"
variant = "full"

[system-info]
os = "macOS 15.3.0 (24D60)"
chip = "Apple M1"
total-cores = 8
memory = "16.00 GB"

[environment]
cwd = "/Users/USER"
cli-path = "/Users/USER"
os = "Mac"
shell-path = "/bin/zsh"
shell-version = "5.9"
terminal = "macOS"
install-method = "unknown"

[env-vars]
PATH = "/Users/USER/.local/share/mise/installs/node/18.20.2/bin:/Users/USER/.local/share/mise/installs/python/3.12.8/bin:/Users/USER/.local/share/mise/installs/python/3.11.11/bin:/Users/USER/.local/share/mise/installs/python/3.10.16/bin:/Users/USER/.local/share/mise/installs/python/3.9.21/bin:/Users/USER/.local/share/mise/installs/python/3.8.20/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/Users/USER/.cargo/bin:/Users/USER/.local/bin:/Applications/Visual Studio Code.app/Contents/Resources/app/bin:/Users/USER/.toolbox/bin:/Users/USER/Library/Python/3.x/bin:/Users/USER/Library/Python/3.13/bin"
QTERM_SESSION_ID = "b47caa71bc6340bd9f19b78dec7f525f"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "1.7.3"
SHELL = "/bin/zsh"
TERM = "xterm-256color"
__CFBundleIdentifier = "com.apple.Terminal"

[chat-settings]
interactive=true

[chat-trusted_tools]

[chat-failed_request_ids]
none

[chat-context]
current_profile=default
profiles=
default

global_context=
.amazonq/rules/**/*.md
README.md
AmazonQ.md

profile_context=none

files=none
```