[P3][docs] Add deterministic Bash completion for published CLIs #1952

Goal

Provide discoverable Bash completion for the published Data Boar CLI surface. The repository already carries the canonical docs/data_boar.1 and docs/data_boar.5 manual pages and an established installation/setup procedure; this issue must reuse those sources and must not duplicate or recreate them.

Scope

• Add deterministic Bash completion for the real [project.scripts] commands: data-boar, data-boar-report, data-boar-xlsx, data-boar-pdf, data-boar-docx, data-boar-heatmap, data-boar-dsar, and data-boar-audit.
• Complete only known commands/flags/values; never expand target data, execute commands, or weaken input validation.
• Keep completion synchronized with docs/data_boar.1, docs/data_boar.5, argparse/Click, and the actual entry points.
• Integrate with issue [P3][ci][docs] Anti-drift CLI(argparse)↔docs + paridade i18n por sufixo .pt_BR.md (origem: análise Gemini) #1448 anti-drift work where appropriate.
• Reuse the existing installation/setup procedure. Add only the minimal completion discovery/install hook if the actual implementation requires one; do not create a parallel setup path.
• Prefer a small deterministic completion implementation over adding a dependency solely for completion.

Acceptance criteria

• Local Bash completion works for the supported command surface and flags.
• Completion is consistent with the existing man 1/man 5 contract and does not recreate those pages.
• Tests or deterministic checks fail when a public entry point or documented flag drifts without updating the completion inventory.
• The existing installation/setup procedure remains the canonical path; no duplicate setup documentation is introduced.
• No change to product behavior or security validation is required.
• Work is issue-first and can be batched with the current documentation/CLI epic; no micro-PR.