Feature request: File-based prompts lack structured argument support

### 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 15.7.0 (24G222)

### Expected behaviour

File-based prompts should support structured arguments like MCP prompts, including argument validation, required/optional distinctions, and metadata display in /prompts list.

### Actual behaviour

Here is my file-based prompt

``` txt
~/.aws/amazonq/prompts/GetDateYYYYMMDD.md

# Get date

Show only date in {time}
format: YYYYMMDD

Don't show anything except date
```

Here is result when run `/prompt list` comparing file-based prompt vs prompt from mcp server with the same prompt:

``` txt
Prompt Description Arguments (* = required)
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Global (.aws/amazonq/prompts):
- GetDateYYYYMMDD

prompt-server (MCP):
- MCP-GetDateYYYYMMDD Get date time*
```

When run `@GetDateYYYYMMDD yesterday`

```
> @GetDateYYYYMMDD yesterday

# Get date

Show only date in {time}
format: YYYYMMDD

Don't show anything except date

🛠️ Using tool: execute_bash
⋮
● I will run the following shell command: date +%Y%m%d
⋮
↳ Purpose: Get current date in YYYYMMDD format

Allow this action? Use 't' to trust (always allow) this tool for the session. [y/n/t]:

[vanilla] > y

20250930

⋮
● Completed in 0.33s

> 20250930
```

When run `@MCP-GetDateYYYYMMDD yesterday`

```
> @MCP-GetDateYYYYMMDD yesterday

# Get date

Show only date in yesterday
format: YYYYMMDD

Don't show anything except date

🛠️ Using tool: execute_bash
⋮
● I will run the following shell command: date -v-1d +%Y%m%d
⋮
↳ Purpose: Get yesterday's date in YYYYMMDD format

Allow this action? Use 't' to trust (always allow) this tool for the session. [y/n/t]:

[vanilla] > y

20250929

⋮
● Completed in 0.43s

> 20250929
```

### Steps to reproduce

1. Create file-based prompt with {language} and {name} placeholders
2. Use prompt with missing arguments
3. No validation occurs
4. /prompts list shows no argument information

### Environment

```yaml

[q-details]
version = "1.16.2"
hash = "c4c80bb44cb22b6e19129ed7475f2793ff20135d"
date = "2025-09-19T01:27:56.356289Z (11d ago)"

[system-info]
os = "macOS 15.7.0 (24G222)"
chip = "Apple M3 Pro"
total-cores = 11
memory = "18.00 GB"

[environment]
cwd = "/Users/USER/Code/amazon-q-developer/references/amazon-q-developer-cli"
cli-path = "/Users/USER/Code/amazon-q-developer/references/amazon-q-developer-cli"
install-method = "unknown"

[env-vars]
PATH = "/Users/USER/.nvm/versions/node/v22.15.1/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:/Applications/iTerm.app/Contents/Resources/utilities:/Users/USER/.local/bin:/Users/USER/.local/bin:/Applications/Visual Studio Code.app/Contents/Resources/app/bin:/Users/USER/.local/bin:/Users/USER/.toolbox/bin"
QTERM_SESSION_ID = "4e61b01d6f784ad7a57e6a6a070e7d6e"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "1.16.2"
SHELL = "/bin/zsh"
TERM = "xterm-256color"
__CFBundleIdentifier = "com.googlecode.iterm2"

[chat-settings]

[chat-trusted_tools]
@calculator=trusted
@awslabs.aws-pricing-mcp-server=trusted
@fetch=trusted
fs_read=trusted
@awslabs.aws-api-mcp-server/suggest_aws_commands=trusted
@awslabs.aws-documentation-mcp-server=trusted
execute_bash=trusted
@aws-knowledge-mcp-server=trusted
@awslabs.core-mcp-server=trusted

[chat-failed_request_ids]
none

[chat-context]
current_profile=default
profile_context=
/Users/sawitmee/Library/CloudStorage/OneDrive-amazon.com/sawitmee/Q-Context/based.md

files=
/Users/sawitmee/Library/CloudStorage/OneDrive-amazon.com/sawitmee/Q-Context/based.md, 70 tkns
total context size=70 tkns
```