refactor(docs): normalize documentation naming to lowercase for PEP8 compliance (#434)

* refactor(docs): rename directories to lowercase for PEP8 compliance

- Developer-Guide → developer-guide
- Getting-Started → getting-started
- Reference → reference
- Templates → templates
- User-Guide → user-guide
- User-Guide-jp → user-guide-jp
- User-Guide-kr → user-guide-kr
- User-Guide-zh → user-guide-zh

This change aligns with Python PEP8 package naming conventions.
All 43 files affected.

* refactor: rename root documentation files to lowercase

- CHANGELOG.md → changelog.md
- CODE_OF_CONDUCT.md → code_of_conduct.md
- CONTRIBUTING.md → contributing.md
- SECURITY.md → security.md

Aligns with Python package naming conventions (PEP8).
README files remain uppercase as per convention.

* refactor: move documentation files to docs/ for cleaner root

Moved OSS standard files to docs/:
- CHANGELOG.md → docs/CHANGELOG.md
- CODE_OF_CONDUCT.md → docs/CODE_OF_CONDUCT.md
- CONTRIBUTING.md → docs/CONTRIBUTING.md
- SECURITY.md → docs/SECURITY.md

Root now contains only essential files:
✓ README files (表紙: en, ja, kr, zh)
✓ LICENSE (法的要件)
✓ Build configs (pyproject.toml, setup.py, MANIFEST.in)
✓ VERSION

Rationale:
Cleaner root structure following modern Python project conventions.
All detailed documentation consolidated in docs/ directory.

* refactor: update documentation links after restructure

Auto-updated internal documentation links to reflect new structure:
- docs/ subdirectories now lowercase (PEP8)
- Root files moved to docs/
- All cross-references updated

This commit includes linter-generated link updates.

* chore(docs): keep OSS-standard uppercase root files (CHANGELOG, CODE_OF_CONDUCT, CONTRIBUTING, SECURITY)

* chore(docs): remove duplicated PR docs from repo root (moved under docs)

* docs: rename pm-agent-implementation-status.md -> PM_AGENT.md for clarity

* docs: update links to PM_AGENT.md after rename

---------

Co-authored-by: kazuki <kazuki@kazukinoMacBook-Air.local>

docs/Development/ROADMAP.md

@@ -31,7 +31,7 @@ Transform SuperClaude into a self-improving development platform with PM Agent m
 
 ### Tasks
 
-- [x] Create `docs/Development/` directory structure
+- [x] Create `docs/development/` directory structure
 - [x] Write `ARCHITECTURE.md` - System overview with PM Agent position
 - [x] Write `ROADMAP.md` - Phase-based development plan with checkboxes
 - [ ] Write `TASKS.md` - Current task tracking system
@@ -40,11 +40,11 @@ Transform SuperClaude into a self-improving development platform with PM Agent m
 
 ### Deliverables
 
-- [x] **docs/Development/ARCHITECTURE.md** - Complete system architecture
-- [x] **docs/Development/ROADMAP.md** - This file (development roadmap)
-- [ ] **docs/Development/TASKS.md** - Task management with checkboxes
-- [ ] **docs/Development/PROJECT_STATUS.md** - Current status and metrics
-- [ ] **docs/Development/pm-agent-integration.md** - Integration procedures
+- [x] **docs/development/ARCHITECTURE.md** - Complete system architecture
+- [x] **docs/development/ROADMAP.md** - This file (development roadmap)
+- [ ] **docs/development/TASKS.md** - Task management with checkboxes
+- [ ] **docs/development/PROJECT_STATUS.md** - Current status and metrics
+- [ ] **docs/development/pm-agent-integration.md** - Integration procedures
 
 ### Success Criteria
 
@@ -69,9 +69,9 @@ Transform SuperClaude into a self-improving development platform with PM Agent m
 #### Documentation Updates
 - [x] Update `superclaude/Commands/pm.md` with Session Lifecycle
 - [x] Update `superclaude/Agents/pm-agent.md` with PDCA Cycle
-- [x] Create `docs/pm-agent-implementation-status.md`
-- [ ] Update `docs/User-Guide/agents.md` - Add PM Agent section
-- [ ] Update `docs/User-Guide/commands.md` - Add /sc:pm command
+- [x] Create `docs/PM_AGENT.md`
+- [ ] Update `docs/user-guide/agents.md` - Add PM Agent section
+- [ ] Update `docs/user-guide/commands.md` - Add /sc:pm command
 
 #### Core Implementation
 - [ ] Implement `superclaude/Core/session_lifecycle.py`
@@ -100,7 +100,7 @@ Transform SuperClaude into a self-improving development platform with PM Agent m
 ### Deliverables
 
 - [x] **Updated pm.md and pm-agent.md** - Design documentation
-- [x] **pm-agent-implementation-status.md** - Status tracking
+- [x] **PM_AGENT.md** - Status tracking
 - [ ] **superclaude/Core/session_lifecycle.py** - Session management
 - [ ] **superclaude/Core/pdca_engine.py** - PDCA automation
 - [ ] **superclaude/Core/memory_ops.py** - Memory operations
@@ -269,7 +269,7 @@ Transform SuperClaude into a self-improving development platform with PM Agent m
 ### Deliverables
 
 - [ ] **superclaude/Core/auto_activation.py** - Auto-activation system
-- [ ] **docs/Developer-Guide/auto-activation.md** - Implementation guide
+- [ ] **docs/developer-guide/auto-activation.md** - Implementation guide
 - [ ] **tests/test_auto_activation.py** - Auto-activation tests
 - [ ] **Performance Report** - Startup time impact analysis