Support for general plain text files in /knowledge feature

### 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 14.7.3 (23H417)

### Expected behaviour

Proper content extraction of any plaint text file when using `/knowledge add ~/dir/with/org-files/`

### Actual behaviour

Files are indexed but content isn't searchable. Tested with .org files, [Org mode](https://orgmode.org) files are plain text files

### Steps to reproduce

given a directory with .org files
when I try to add them with `/knowledge add ~/dir/with/org-files/`
then I see the knowledge base is created
and it shows the correct number of files
but the content of the files is not searchable

when I export the .org file into an .md file, then the content is searchable after being added to a knowledge base

### Environment

```yaml

[q-details]
version = "1.17.1"
hash = "b0ef39f91625c36c2ed6f065628e7165fae9012c"
date = "2025-09-30T22:01:25.726592Z (8d ago)"

[system-info]
os = "macOS 14.7.3 (23H417)"
chip = "Intel(R) Core(TM) i5-1038NG7 CPU @ 2.00GHz"
total-cores = 4
memory = "16.00 GB"

[environment]
cwd = "/Users/USER/dotfiles"
cli-path = "/Users/USER/dotfiles"
install-method = "brew"

[env-vars]
DISPLAY = "/private/tmp/com.apple.launchd.Qc8BNsUCi2/org.xquartz:0"
PATH = "~/bin:/usr/local/bin:/Library/TeX/Distributions/Programs/texbin:/Users/USER/.rbenv/shims:/Users/USER/.nvm/versions/node/v12.19.1/bin:/opt/local/bin:/opt/local/sbin:/usr/local/opt/jenv/shims:/Users/USER/.jenv/bin:/usr/local/sbin:/usr/local/Cellar/gnupg@2.2.41/2.2.41/bin:/usr/local/git/bin:/Users/USER/.pyenv/plugins/pyenv-virtualenv/shims:/Users/USER/.pyenv/shims:/Users/USER/.pyenv/bin:~/go/bin:/Users/USER/.basher/cellar/bin:/Users/USER/.basher/bin:~/bin:/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:/opt/X11/bin:/Library/Apple/usr/bin:~/bin:/Library/TeX/Distributions/Programs/texbin:/opt/local/bin:/opt/local/sbin:/usr/local/opt/jenv/shims:/Users/USER/.jenv/bin:/usr/local/sbin:/usr/local/Cellar/gnupg@2.2.41/2.2.41/bin:/usr/local/git/bin:/Users/USER/.pyenv/plugins/pyenv-virtualenv/shims:/Users/USER/.pyenv/shims:/Users/USER/.pyenv/bin:~/go/bin:/Users/USER/.basher/cellar/bin:/Users/USER/.basher/bin:/Users/USER/.nvm/versions/node/v12.19.1/bin:/Applications/iTerm.app/Contents/Resources/utilities:/Users/USER/.rvm/bin:/Users/USER/.local/bin:/Users/USER/.rvm/bin"
QTERM_SESSION_ID = "e6217365b5744ceba492bab4c36f5ae7"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "1.16.1"
SHELL = "/bin/bash"
TERM = "tmux-256color"
__CFBundleIdentifier = "com.googlecode.iterm2"
```