ctx-convention-add

Record a coding convention in CONVENTIONS.md.

## When to Use

- When a pattern has been used 2-3 times and should be standardized
- When establishing a naming, formatting, or structural rule
- When a new contributor would need to know "how we do things here"
- When the user says "codify that" or "make that a convention"

## When NOT to Use

- One-off implementation details (use code comments instead)
- Architectural decisions with trade-offs (use `/ctx-decision-add`)
- Debugging insights or gotchas (use `/ctx-learning-add`)
- Rules that are already enforced by linters or formatters

## Gathering Information

Conventions are simpler than decisions or learnings. You need:

1. **Name**: What is the convention called? (e.g., "kebab-case CLI flags")
2. **Rule**: What is the rule? One clear sentence.
3. **Section**: Where does it belong in CONVENTIONS.md? (e.g., "Naming",
   "Output", "Testing")

If the user provides only a description, infer the section from the
topic. Check existing sections in CONVENTIONS.md first to place it
correctly: don't create a new section if an existing one fits.

If the convention overlaps with an existing one, mention it:
*"There's already a naming convention for functions. Want me to add
this alongside it or update the existing one?"*

## Execution

```bash
ctx add convention "Use kebab-case for all CLI flag names" --section "Naming"
```

```bash
ctx add convention "Use cmd.Printf/cmd.Println for CLI output, never fmt.Printf/fmt.Println" --section "Output"
```

```bash
ctx add convention "Colocate test files with implementation (*_test.go next to *.go)" --section "Testing"
```

If no `--section` is provided, the convention is appended to the end
of the file. Prefer specifying a section for organization.

## Quality Checklist

Before recording, verify:
- [ ] The rule is clear enough that someone unfamiliar could follow it
- [ ] It is specific to this project (not a general Go/JS/etc. rule)
- [ ] It is not already in CONVENTIONS.md (check first)
- [ ] The section matches an existing section, or a new section is
      genuinely needed
- [ ] It describes a pattern, not a one-time choice (that's a decision)

Confirm the convention was added.