Downgrade golangci-lint action to v6 to support v1.x

golangci-lint-action@v6 supports golangci-lint v1.x
golangci-lint-action@v8 requires v2.x which has breaking config changes
Downgrading to v6 allows us to use stable v1.x release
Removed version field from .golangci.yml (not needed for v1.x)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: kevinelliott

.github/workflows/test.yml

@@ -63,7 +63,7 @@ jobs:
           go-version: '1.24'
 
       - name: Run golangci-lint
-        uses: golangci/golangci-lint-action@v8
+        uses: golangci/golangci-lint-action@v6
         with:
           version: latest
           args: --timeout=5m

.golangci.yml

@@ -1,4 +1,3 @@
-version: 2
 run:
   timeout: 5m
   tests: true

CLAUDE.md

@@ -24,14 +24,14 @@ AgentPipe is a CLI and TUI application that orchestrates conversations between m
 ### CI/CD Configuration
 
 #### Linting
-- Use golangci-lint-action@v8 with golangci-lint v1.64.8 (stable v1.x)
-- GitHub Action version parameter: `version: v1.64.8` (pinned for reproducibility)
-- **IMPORTANT**: Config file (`.golangci.yml`) uses v1.x format (no version field required)
+- Use golangci-lint-action@v6 with golangci-lint v1.x (latest stable)
+- GitHub Action version parameter: `version: latest` (downloads latest v1.x)
+- **IMPORTANT**: Config file (`.golangci.yml`) uses v1.x format (no version field)
 - **Note**: Removed `nakedret` linter (removed in v2.x, compatible with v1.x)
-- **Status**: v2.5.0 (latest) has config compatibility issues; v1.64.8 is stable
-- **Local linting**: Install golangci-lint v1.64.8
+- **Status**: v2.x requires config schema changes; staying on v1.x is more stable
+- **Local linting**: Install latest golangci-lint v1.x
   - Install: `brew install golangci-lint`
-  - Or: `go install github.com/golangci/golangci-lint/cmd/golangci-lint@v1.64.8`
+  - Or: `go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest`
 - Configuration structure: `linters-settings:` for linter config, `issues.exclude-rules:` for exclusions
 - Cognitive complexity threshold: 30
 - Excluded from complexity checks: pkg/tui/, pkg/adapters/, pkg/orchestrator/