feat: flag plural nouns followed by seems

[ColumbusLabs]

This pull request was implemented and tested by an autonomous OpenAI Codex agent.

Issues

Fixes #3285.

Description

Adds a focused agreement rule for unambiguously plural common nouns followed by seems, replacing the verb with seem while preserving its case.

The rule is intentionally conservative around prepositional phrases, coordinated noun lists, mass nouns, proper nouns, and singular/plural-invariant nouns to avoid default-enabled false positives. It validates regular and curated irregular plural forms before reporting.

Demo

Web pages seems to work pretty well so far. is reported as PluralNounSeems with the correction Web pages seem to work pretty well so far.

How Has This Been Tested?

• cargo test -p harper-core plural_noun_seems -- --nocapture (19 passed)
• just test-rust (6,107 passed, 290 ignored, 0 failed in harper-core; all workspace tests and doctests passed)
• just format
• cargo fmt --all -- --check
• git diff --check
• cargo run --bin harper-cli --release -- lint 'Web pages seems to work pretty well so far.'

just check-rust was also attempted. It reached the workspace Clippy pass but is currently blocked on existing harper-desktop/src-tauri/src/mac_broker/mod.rs:34 (Config is an unused import under -D warnings), outside this change.

AI Disclosure

• I am a human and didn't use any AI.
• I used LLM features of my editor, but not an agent.
• I consulted one or more coding AIs, but didn't use an agent.
• I used an AI agent interactively.
• I am an agent or I got an agent to do the work autonomously.

If Your PR Implements or Enhances a Linter

• I made up the sentences in the unit tests.
• The sentences in the unit tests were generated by an AI.
• I'm using examples from the bug report / feature request.
• I collected real-world sentences for the unit tests.

Checklist

• I have performed a self-review of my own code
• I have added tests to cover my changes
• I have considered splitting this into smaller pull requests.