ci: add typo, packaging, and API coverage guardrails

[philippemnoel]

Ticket(s) Closed

• Closes #

What

• adds a repository-level .codespellrc and wires typo checks to use it
• adds a new API consistency check script: scripts/check_api_coverage.rb
• adds a new gem packaging/install smoke script: scripts/smoke_gem_install.sh
• runs both new consistency checks in CI lint job
• adds a codespell pre-commit hook and documents the new checks in CONTRIBUTING.md

Why

• centralize typo-check configuration for easier maintenance
• catch API drift between wrappers and api.json/apiignore.json earlier in CI
• ensure packaged gem artifacts can be built and installed cleanly
• strengthen repo-level quality guardrails similarly to django-paradedb

How

• replaced the typo workflow action step with explicit codespell CLI execution against .codespellrc
• implemented API coverage validation for operators/functions/types and untracked pdb symbols
• implemented a smoke script that builds the gem, installs it into an isolated GEM_HOME, and executes a runtime sanity check
• added CI lint steps to execute both scripts

Tests

• ruby scripts/check_api_coverage.rb
• bash -n scripts/smoke_gem_install.sh
• smoke install script execution was attempted, but local environment Ruby is 2.6.10 (repo requires >= 3.2), so full runtime smoke validation is left to CI Ruby matrix