chore: Bump version to 0.26.0

Release highlights:
- bd doctor --check-health for lightweight startup hook health checks
- --no-git-history flag to prevent spurious deletions
- gh2jsonl --id-mode hash for content-based ID generation
- Critical MCP protocol stdin fix (PR #400)
- Git worktree staleness fix (#399)
- Multi-part prefix support (#398)
- bd sync commit scope fix

Updated all component versions:
- bd CLI: 0.25.1 -> 0.26.0
- Plugin: 0.25.1 -> 0.26.0
- MCP server: 0.25.1 -> 0.26.0
- npm package: 0.25.1 -> 0.26.0

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

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

cmd/bd/version.go

@@ -14,7 +14,7 @@ import (
 
 var (
 	// Version is the current version of bd (overridden by ldflags at build time)
-	Version = "0.25.1"
+	Version = "0.26.0"
 	// Build can be set via ldflags at compile time
 	Build = "dev"
 	// Commit and branch the git revision the binary was built from (optional ldflag)