Add Bugfix Workflow community extension to catalog and README

[Quratulain-bilal]

Summary

• Adds bugfix entry to extensions/catalog.community.json (alphabetically between branch-convention
  and canon)
• Adds Bugfix Workflow row to README.md Community Extensions table (alphabetically between Branch Convention and Canon)

Extension Details

Field	Value
ID	bugfix
Name	Bugfix Workflow
Commands	3 (report, patch, verify)
Hooks	1 (after_implement)
Category	process
Effect	Read+Write
Requires	spec-kit >= 0.4.0
Repository	https://github.com/Quratulain-bilal/spec-kit-bugfix

What It Does

Structured bugfix workflow for when bugs surface during implementation — addresses issue #619 (25+
upvotes), where the maintainer explicitly said "Go for it and do it as an extension!"

• /speckit.bugfix.report — Capture a bug and trace it back to spec, plan, and task artifacts with full
  traceability
• /speckit.bugfix.patch — Surgically update spec, plan, and tasks to address the reported bug (never
  regenerates from scratch)
• /speckit.bugfix.verify — Verify consistency across all artifacts after patching (read-only)

Bug classification: spec gap, spec conflict, implementation drift, untested flow, dependency issue.

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
• 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)

Closes #619