Load rubocop-rake and rubocop-rspec plugins (herb-embedded-5g1)

[jleo3]

Summary

• rubocop-rake/rubocop-rspec were already dev dependencies but never actually loaded (require: false, no require/plugins key in .rubocop.yml) — hence RuboCop's own "extension libraries are installed but not loaded" suggestion. Adds a plugins: key (the modern mechanism, per docs.rubocop.org/rubocop/plugins.html) to actually load both.
• rubocop-rake found nothing (Rakefile/rakelib are small). rubocop-rspec surfaced 136 offenses across 11 cops — addressed as a mix of real fixes and documented configuration, not a blanket disable.

Fixed:

• include_examples → it_behaves_like (verified safe — the shared example group's bare subject still resolves correctly through the nested context).
• Named an anonymous subject.
• Converted a message expectation to the spy pattern (allow/have_received).
• Split report_spec.rb's two top-level describes into report_spec.rb and lint_result_spec.rb — also fixes a pre-existing violation of CLAUDE.md's own "one spec file per lib unit" convention.
• Applied safe autocorrects for scattered lets and simple-regex-as-string matchers.

Configured (each with a comment explaining why):

• RSpec/SpecFilePathFormat disabled — this suite's spec/ is deliberately flat, not nested to mirror lib/'s namespace dirs.
• RSpec/ExampleLength/RSpec/MultipleExpectations raised to 25/8 — picked after checking the actual worst offenders (22 lines / 7 expectations), not arbitrary; this suite favors thorough, narrative examples over one-assertion-per-it.
• RSpec/DescribeClass excluded for the three specs that describe a scenario or guarantee rather than one Ruby class.
• One inline (not global) disable for RSpec/LeakyLocalVariable where the flagged pattern is a per-.each-iteration closure local, not the cross-example leak the cop targets.

Acceptance criteria

• rubocop-rake/rubocop-rspec in the Gemfile dev group and Gemfile.lock — already present from a prior bead.
• Both listed under a plugins: key in .rubocop.yml.
• bundle exec rake runs clean — no "extension libraries" nag, and every offense fixed or explicitly configured with reasoning.
• Full local gate passes: 45 files, 0 RuboCop offenses, 206 examples, 0 failures, no vulnerabilities.

Test plan

• bundle exec rake (RuboCop + full RSpec suite + bundler-audit) passes locally.
• Each it_behaves_like conversion re-verified in isolation (14 examples, 0 failures) to confirm shared-example subject resolution is unchanged.

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