docs(v2): add missing doc.go files for fields and log packages

See merge request !357



Merged-by: Elliot Forbes <eforbes@gitlab.com>
Approved-by: Elliot Forbes <eforbes@gitlab.com>
Reviewed-by: GitLab Duo <gitlab-duo@gitlab.com>
Co-authored-by: dbarrett <dbarrett@gitlab.com>

refactor(v2/secret): remove deprecated NewClient constructor

See merge request !350



Merged-by: Matias Alvarez <malvarez@gitlab.com>
Approved-by: Matias Alvarez <malvarez@gitlab.com>
Reviewed-by: Doug Barrett <dbarrett@gitlab.com>
Co-authored-by: e_forbes <eforbes@gitlab.com>

docs(v2): add Example_ functions for pkg.go.dev discoverability

See merge request !348



Merged-by: Bob Van Landuyt <bob@gitlab.com>
Approved-by: Bob Van Landuyt <bob@gitlab.com>
Reviewed-by: Matias Alvarez <malvarez@gitlab.com>
Co-authored-by: e_forbes <eforbes@gitlab.com>

Add .gitlab/duo/mr-review-instructions.yaml with review instructions
tailored to LabKit's architecture. Duo will apply these automatically
when reviewing MRs, focusing on higher-order concerns that linters
cannot catch.

Instruction groups:
- LabKit v2 Architecture (interface design, lifecycle, concurrency)
- LabKit v2 Tests (isolation, testify patterns, table-driven tests)
- LabKit v1 Root Module (backward compat only, no new API surface)
- Shell Scripts (strict mode, quoting, structure)
- GitLab CI Configuration (DAG, rules, two-module testing)
- Markdown Documentation (LabKit README conventions, style)
- Dependency Management (two-module go.mod, minimize deps)
- Conventional Commits (scopes, header length)

- POSIX strict mode: use portable 'set -eu' instead of 'set -o errexit'
- Bash conditionals: prefer [[ ]] but allow [ ] for POSIX compatibility
- Error strings: focus on Go conventions (no capitals, no trailing
  punctuation, add context) rather than banning specific words

ci: add GitLab Duo code review instructions

See merge request !365



Merged-by: Elliot Forbes <eforbes@gitlab.com>
Approved-by: Elliot Forbes <eforbes@gitlab.com>
Reviewed-by: GitLab Duo <gitlab-duo@gitlab.com>
Co-authored-by: dbarrett <dbarrett@gitlab.com>