refactor(skills): migrate commands to skills directory structure

Move all 27 command .md files from commands/ to skills/*/SKILL.md
format. Claude Code 2.1.3+ merged commands and skills - both create
slash commands and work identically. Skills add optional features
like supporting files and automatic context loading.

- commands/ce/*.md -> skills/ce-*/SKILL.md
- commands/workflows/*.md -> skills/workflows-*/SKILL.md
- commands/*.md -> skills/*/SKILL.md
- Update plugin.json and marketplace.json descriptions
- Update CLAUDE.md directory structure docs
- Update deploy-docs and generate_command references

Fixes #116

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/compound-engineering/commands/workflows/brainstorm.md

@@ -1,10 +0,0 @@
----
-name: workflows:brainstorm
-description: "[DEPRECATED] Use /ce:brainstorm instead — renamed for clarity."
-argument-hint: "[feature idea or problem to explore]"
-disable-model-invocation: true
----
-
-NOTE: /workflows:brainstorm is deprecated. Please use /ce:brainstorm instead. This alias will be removed in a future version.
-
-/ce:brainstorm $ARGUMENTS

plugins/compound-engineering/commands/workflows/compound.md

@@ -1,10 +0,0 @@
----
-name: workflows:compound
-description: "[DEPRECATED] Use /ce:compound instead — renamed for clarity."
-argument-hint: "[optional: brief context about the fix]"
-disable-model-invocation: true
----
-
-NOTE: /workflows:compound is deprecated. Please use /ce:compound instead. This alias will be removed in a future version.
-
-/ce:compound $ARGUMENTS

plugins/compound-engineering/commands/workflows/plan.md

@@ -1,10 +0,0 @@
----
-name: workflows:plan
-description: "[DEPRECATED] Use /ce:plan instead — renamed for clarity."
-argument-hint: "[feature description, bug report, or improvement idea]"
-disable-model-invocation: true
----
-
-NOTE: /workflows:plan is deprecated. Please use /ce:plan instead. This alias will be removed in a future version.
-
-/ce:plan $ARGUMENTS

plugins/compound-engineering/commands/workflows/review.md

@@ -1,10 +0,0 @@
----
-name: workflows:review
-description: "[DEPRECATED] Use /ce:review instead — renamed for clarity."
-argument-hint: "[PR number, GitHub URL, branch name, or latest]"
-disable-model-invocation: true
----
-
-NOTE: /workflows:review is deprecated. Please use /ce:review instead. This alias will be removed in a future version.
-
-/ce:review $ARGUMENTS

plugins/compound-engineering/commands/workflows/work.md

@@ -1,10 +0,0 @@
----
-name: workflows:work
-description: "[DEPRECATED] Use /ce:work instead — renamed for clarity."
-argument-hint: "[plan file, specification, or todo file path]"
-disable-model-invocation: true
----
-
-NOTE: /workflows:work is deprecated. Please use /ce:work instead. This alias will be removed in a future version.
-
-/ce:work $ARGUMENTS