Add Spec Refine community extension to catalog and README

[Quratulain-bilal]

Summary

• Adds refine entry to extensions/catalog.community.json (alphabetically between reconcile and
  repoindex)
• Adds Spec Refine row to README.md Community Extensions table (alphabetically between Spec Critique Extension and Spec Sync)
• Updates catalog updated_at timestamp

Extension Details

Field	Value
ID	refine
Name	Spec Refine
Commands	4 (update, propagate, diff, status)
Hooks	2 (after_specify, after_plan)
Category	process
Effect	Read+Write
Requires	spec-kit >= 0.4.0
Repository	https://github.com/Quratulain-bilal/spec-kit-refine

What It Does

Enables iterative specification refinement — the #1 most-requested feature (issue #1191, 101+ upvotes):

• /speckit.refine.update — Update spec.md in-place based on new requirements or feedback
• /speckit.refine.propagate — Cascade spec changes downstream to plan.md and tasks.md
• /speckit.refine.diff — Preview downstream impact before propagating (read-only)
• /speckit.refine.status — Artifact sync dashboard showing stale/current/missing status (read-only)

Checklist

• Entry added to extensions/catalog.community.json in alphabetical order by ID
• Row added to README.md Community Extensions table in alphabetical order by name
• Catalog updated_at timestamp updated
• JSON validates successfully
• Extension repo has valid extension.yml, all command files, README, CHANGELOG, and LICENSE
• verified: false, downloads: 0, stars: 0 set for new submission
• Only 2 files modified (catalog + README)
  Allow edits and access to secrets by maintainers
  Remember, contributions to this repository should follow its contributing guidelines, security policy, and code of conduct.
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Closes #1191

[Quratulain-bilal]

Hi @mnriem 👋 This addresses issue #1191 (101+ upvotes) — the most-requested feature for iterative spec refinement. Would love your feedback when you get a chance!