feat: Add version bump script for consistent versioning

Adds scripts/bump-version.sh to automate version syncing across all
beads components, preventing version mismatches like bd-66.

Features:
- Updates all version files in one command
- Validates semantic versioning format
- Verifies all versions match after update
- Shows git diff preview
- Optional auto-commit with standardized message
- Cross-platform compatible (macOS/Linux)

Files updated by script:
- cmd/bd/version.go
- .claude-plugin/plugin.json
- .claude-plugin/marketplace.json
- integrations/beads-mcp/pyproject.toml
- README.md
- PLUGIN.md

Usage:
  ./scripts/bump-version.sh 0.9.3           # Dry run with diff
  ./scripts/bump-version.sh 0.9.3 --commit  # Auto-commit

Closes bd-67

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

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

scripts/README.md

@@ -0,0 +1,66 @@
+# Beads Scripts
+
+Utility scripts for maintaining the beads project.
+
+## bump-version.sh
+
+Bumps the version number across all beads components in a single command.
+
+### Usage
+
+```bash
+# Show usage
+./scripts/bump-version.sh
+
+# Update versions (shows diff, no commit)
+./scripts/bump-version.sh 0.9.3
+
+# Update versions and auto-commit
+./scripts/bump-version.sh 0.9.3 --commit
+```
+
+### What It Does
+
+Updates version in all these files:
+- `cmd/bd/version.go` - bd CLI version constant
+- `.claude-plugin/plugin.json` - Plugin version
+- `.claude-plugin/marketplace.json` - Marketplace plugin version
+- `integrations/beads-mcp/pyproject.toml` - MCP server version
+- `README.md` - Alpha status version
+- `PLUGIN.md` - Version requirements
+
+### Features
+
+- **Validates** semantic versioning format (MAJOR.MINOR.PATCH)
+- **Verifies** all versions match after update
+- **Shows** git diff of changes
+- **Auto-commits** with standardized message (optional)
+- **Cross-platform** compatible (macOS and Linux)
+
+### Examples
+
+```bash
+# Bump to 0.9.3 and review changes
+./scripts/bump-version.sh 0.9.3
+# Review the diff, then manually commit
+
+# Bump to 1.0.0 and auto-commit
+./scripts/bump-version.sh 1.0.0 --commit
+git push origin main
+```
+
+### Why This Script Exists
+
+Previously, version bumps only updated `cmd/bd/version.go`, leaving other components out of sync. This script ensures all version numbers stay consistent across the project.
+
+### Safety
+
+- Checks for uncommitted changes before proceeding
+- Refuses to auto-commit if there are existing uncommitted changes
+- Validates version format before making any changes
+- Verifies all versions match after update
+- Shows diff for review before commit
+
+## Future Scripts
+
+Additional maintenance scripts may be added here as needed.