feat: typed property values via --type flag for set command

[flyingrobots]

Context

git mind set currently treats all <value> arguments as strings (documented in GUIDE.md as of #222). The idempotency check uses strict equality (===), which works for strings but would always report changed: true for objects/arrays. This is fine for the current CLI use case (status values like done, in-progress) but limits programmatic use.

Proposal

Add an optional --type flag to git mind set:

git mind set task:a priority 3 --type number
git mind set task:a archived true --type bool
git mind set task:a metadata '{"key":"val"}' --type json

Types:

• string (default, current behavior)
• number — parseFloat(value), error on NaN
• bool — true/false only
• json — JSON.parse(value), error on invalid JSON

The idempotency check in setNodeProperty would need a deep-equality path for structured values (e.g. util.isDeepStrictEqual).

Acceptance Criteria

• --type number|bool|json flag parsed and validated
• setNodeProperty uses deep equality when value is non-primitive
• set.schema.json updated to allow non-string value field
• Tests cover each type + error cases
• Backward compatible — omitting --type preserves string behavior

Originated from PR #223 agent reflection.