ci: split CI into reusable workflows with an orchestrator

[Primajin]

Summary

Retrofits the monolithic `ci.yml` into the reusable-workflow layout, mirroring the merged Gyros exemplar. Each substantive job now lives in its own reusable `_.yml` (`on: workflow_call`), and `ci.yml` becomes a thin orchestrator that calls each one and aggregates results into a single `All checks green` gate.

No CI behaviour changes — steps, action versions, Node `'24'`, GPG import, the `peaceiris/actions-gh-pages` deploy, and the `ACTIONS_DEPLOY_KEY`/`CODECOV_TOKEN` secrets are preserved verbatim.

Changes

• New `_jsdoc.yml` — the docs-build-and-deploy job. The job-level `concurrency: gh-pages` was promoted to workflow level so the serialisation still applies when called.
• New `_lint.yml` — the XO lint job (`permissions: write-all`), GPG import step unchanged.
• New `_test.yml` — the coverage/Codecov job (`permissions: contents: read`).
• `ci.yml` — now orchestrates three caller jobs (each keeping its original `if:` and `permissions:`, plus `secrets: inherit`) and the inline `all-green` aggregator over all callers.
• `codeql-analysis.yml` and `release-please.yml` left untouched.

🤖 Generated with Claude Code

[Primajin]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a25c61b) to head (11526bd).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #277   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines           95        95           
=========================================
  Hits            95        95           

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