Rename shared skills with azsdk-common- prefix for sync pipeline (#46413)

Re-creates PR #15062 on a fresh branch off current upstream/main to avoid
sync-pipeline CI issues on the original branch. Original branch
squad/15049-sync-shared-skills and PR #15062 are preserved unchanged for
comparison.

Makes skills the single source of truth by consolidating instruction file
content into the corresponding skill SKILL.md files, then deleting the
redundant instruction files. Also renames 5 shared skill directories with
the 'azsdk-common-' prefix required by the sync pipeline.

7 instruction files deleted (content merged into skills):
- local-sdk-workflow.instructions.md -> azsdk-common-generate-sdk-locally
- create-release-plan.instructions.md -> azsdk-common-prepare-release-plan
- sdk-details-in-release-plan.instructions.md -> azsdk-common-prepare-release-plan
- verify-namespace-approval.instructions.md -> azsdk-common-prepare-release-plan
- check-package-readiness.instructions.md -> azsdk-common-sdk-release
- check-package-validation.instructions.md -> azsdk-common-generate-sdk-locally
- copilot/sdk-release.instructions.md -> azsdk-common-sdk-release

3 skills enriched with details from instruction files:
- generate-sdk-locally: commit checkpoints, language selection, config file
  identification, SDK project path, metadata update tools, validation params
- prepare-release-plan: critical LLM instructions (NextSteps field), Release
  Planner Tool link, per-language package name extraction rules,
  valid/invalid examples table, JSON structure, namespace approval flow
- sdk-release: readiness check details, interaction flow, do-not-ask-for-PR
  guard, case-sensitive language note

5 shared skill directories renamed with 'azsdk-common-' prefix:
  apiview-feedback-resolution, generate-sdk-locally,
  pipeline-troubleshooting, prepare-release-plan, sdk-release

typespec-to-sdk orchestrator updated to reference skills directly. Removed
all related_skill frontmatter and blockquotes.

Co-authored-by: l0lawrence <l0lawrence@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Libba Lawrence <llawrence@microsoft.com>

Author: 3 people