Add optional persona support with first-position output

[Copilot]

Adds optional persona files that render first in prompt.md output, before memories and tasks. Personas define the AI agent's role or character.

Changes

• CLI usage: Persona is specified as an optional positional argument after task name: coding-context <task-name> [persona-name]
• CLI flag: Added -r <path> for persona directories
• Default directories: .prompts/personas, ~/.config/prompts/personas, /var/local/prompts/personas
• Processing order: Persona (if specified) → Memories → Task
• No template expansion: Personas are included as-is without variable substitution
• Error handling: If persona is requested but not found, returns an error
• Tests: Added 3 integration tests covering basic usage, optional usage, and error cases

Usage

# Define persona (no template variables - included as-is)
cat > .prompts/personas/expert.md << 'EOF'
# Expert Developer
You are an expert software engineer with deep knowledge of best practices.
EOF

# Use with task (persona as optional positional argument)
coding-context add-feature expert

Output order in prompt.md:

# Expert Developer (persona first, no variable expansion)
# Project Context (memories)
# Task: Add Feature (task last)

Persona is fully optional - omitting the persona argument produces identical output to current behavior.

Original prompt

I need to support an optional persona too. This should operate in a similar fashion to the task. The persona should be the first output.

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[alexec]

@copilot Use "-r" for the personas. Requesting a persona is optional, but if one is requested, and it in not found, that is an error. Make persona on optional argument after the taskName. Persona don't need expanded variables or filters.

[Copilot]

@copilot Use "-r" for the personas. Requesting a persona is optional, but if one is requested, and it in not found, that is an error. Make persona on optional argument after the taskName. Persona don'...

Done. Changes made in commit 168d6ad:

1. ✅ Changed flag from -P to -r for persona directories
2. ✅ Made persona an optional positional argument after taskName: coding-context <task-name> [persona-name]
3. ✅ Removed template variable expansion from personas - they're now included as-is
4. ✅ Error handling already in place - if persona is requested but not found, returns error

New usage:

coding-context add-feature expert  # with persona
coding-context add-feature         # without persona