Add hierarchical log-category gates and enabled checks

[codeforester]

Problem

base-bash-libs currently uses one logger-level map for terminal visibility,
while BASE_CLI_PRIMARY_LOG independently persists the DEBUG stream. That
supports quiet terminals plus complete diagnostics, but it does not provide a
separate component/category gate. A consuming application therefore cannot
enable its own DEBUG output while explicitly declining reusable-library DEBUG
records, nor can it cheaply test whether an expensive library diagnostic would
reach any sink.

The existing -l <logger> support is exact-only and is not a hierarchical
category contract.

Goal

Add a backward-compatible category gate that is independent from terminal and
persistent sink thresholds.

Scope

• Add set_log_category_level -l <category> <level>.
• Resolve dotted categories in this order:
  1. exact category;
  2. nearest explicitly configured parent;
  3. the category default.
• Keep the default category gate permissive through VERBOSE during the
  compatibility window so existing unscoped callers do not lose records.
• Add log_is_enabled [-l <category>] <level>.
• Require a record to pass its category gate before either the terminal or
  BASE_CLI_PRIMARY_LOG sink can consume it.
• Keep set_log_level as the existing terminal-verbosity API.
• Let unconfigured named terminal loggers inherit the default terminal level,
  while preserving explicit set_log_level -l <logger> <level> overrides.
• Apply the same category and sink decisions to file logging helpers.
• Document the public API and category-versus-sink model.

Acceptance criteria

• Existing unscoped log_* and set_log_level behavior remains compatible.
• Default INFO terminal output plus BASE_CLI_PRIMARY_LOG still persists
  unscoped DEBUG records without printing them.
• Exact category configuration overrides a parent; a parent overrides
  default; sibling categories remain independent.
• A category configured at INFO drops its DEBUG records from both stderr and
  BASE_CLI_PRIMARY_LOG.
• A category configured at DEBUG with an INFO terminal and active primary sink
  persists DEBUG without printing it.
• log_is_enabled returns success only when the category accepts the level and
  at least one configured sink would consume it.
• log_is_enabled and set_log_category_level reject invalid levels and
  malformed -l usage without mutating existing state.
• File logging helpers obey the same category gate.
• Focused BATS tests and the complete repository validation pass.

Non-goals

• Migrating the repository's own log calls to component categories.
• Deprecating or removing VERBOSE.
• Changing rendered log-record formatting.
• Changing Base or Python logging behavior.
• Changing VERSION or publishing a release.

Validation

• Focused coverage in lib/bash/std/tests/lib_std.bats.
• ./tests/validate.sh
• git diff --check

Related work

• Add shared primary diagnostic sink for DEBUG-persistent run logs #185 / PR Add shared primary diagnostic sink for DEBUG-persistent run logs #186 added the shared persistent DEBUG sink whose behavior this
  category gate must preserve.