Make stdlib initialization explicit (#222)

[codeforester]

What changed

• Make lib_std.sh sourcing passive: no positional-argument rewriting, runtime logging/color initialization, traps, exports, or caller-owned runtime globals.
• Add idempotent base_bash_libs_init with explicit source context and caller-owned filtered-argument output.
• Move launcher initialization into bin/base-bash and update library documentation, examples, and companion-library tests.
• Add source-guard and explicit-initialization coverage, including caller shell-state preservation and repeated-init diagnostics.

Why

Sourcing a reusable Bash library should be safe and composable. Runtime configuration now happens at an explicit lifecycle boundary, making direct use, embedding, and composition predictable while preserving wrapper flag behavior in the launcher.

Validation

• ./tests/validate.sh
• 475 BATS tests passed
• Bash 4.2-compatible logging/release smoke checks passed
• All eight Bash option-contract modes passed
• Examples and ShellCheck error profile passed

Fixes #222