feat: support custom properties on beans (Refs: beans-digu)

[hmans]

Summary

Adds support for attaching arbitrary key-value metadata to beans via a properties field in YAML frontmatter.

Bean: beans-digu — "Support custom properties on beans"

Changes

Data Model (internal/bean/bean.go)

• Added Properties map[string]any field to Bean, frontMatter, and renderFrontMatter structs
• Added helper methods: SetProperty(key, value), UnsetProperty(key), GetProperty(key)
• UnsetProperty normalizes empty maps to nil (so omitempty works correctly)
• ETag and MarshalJSON work automatically — no changes needed

GraphQL Schema

• Added scalar JSON mapped to gqlgen built-in graphql.Map
• Added properties: JSON to Bean type and CreateBeanInput
• Added to UpdateBeanInput:
  • properties: JSON — replace all (mutually exclusive with set/unset)
  • setProperties: JSON — merge/upsert specific keys
  • unsetProperties: [String!] — remove specific keys

CLI

• beans create --set key=value (repeatable) — set properties at creation time
• beans update --set key=value --unset key (repeatable) — granular property updates
• beans show — displays properties section between relationships and body
• YAML-based auto type detection: 3→int, true→bool, 4.5→float, text→string

Tests

• Bean model: parse, render, roundtrip (type preservation), helpers, ETag, JSON serialization
• GraphQL resolvers: create with properties, replace-all, set/unset, mutual exclusivity, normalize to nil
• CLI: parsePropertyFlags table-driven tests (string, int, bool, float, empty, errors)

Example Usage

# Create with properties
beans create "Fix auth" -t bug --set estimate=3 --set author=alice --set reviewed=true

# Update properties
beans update <id> --set estimate=5 --unset reviewed

# View properties
beans show <id>        # styled output with properties section
beans show <id> --json # JSON with properties object
beans show <id> --raw  # YAML frontmatter with properties block

YAML Frontmatter

---
title: Fix authentication bug
status: in-progress
type: bug
properties:
    author: alice
    estimate: 3
    reviewed: true
---

Not in scope

• Filtering/searching by property values (future work)
• Property key name validation
• TUI property editing