Add allow_special mode to fully disable specialty keytags (#25)

[dgershman]

Closes #25

What

Adds a mode where specialty/long-term keytags are fully disabled — the in-widget toggle checkbox/label are not rendered and the visitor's saved preference is ignored — rather than the admin setting only controlling the initial state.

Changes

JS (nacc2/src/nacc.js)

• New 7th constructor param allowSpecialTags (default true, back-compat). When false:
  • showSpecialTags is forced off,
  • localStorage['nacc_keytag_special'] and the NACC-special-tags GET param are ignored (a prior visitor toggle or URL param can't re-enable),
  • specialTagsCheckbox / specialTagsLabel are not created (the layout toggle still renders).
• Bundle nacc2/nacc.js rebuilt via vite.

PHP (nacc-wordpress-plugin.php)

• New nacc_allow_special boolean setting (default true) + a "Allow Visitors To Toggle Specialty Keytags" checkbox on Settings → NACC.
• New allow_special shortcode attribute (e.g. [nacc allow_special="0"]), wired through both the standard (trigger_after_shortcode_loaded) and legacy (nacc_content) paths and passed as the 7th JS constructor arg in render_keytags().
• Defaults preserve today's behavior.

readme.txt — documented the allow_special attribute, added a 6.0.2 changelog entry, bumped Stable tag + plugin Version to 6.0.2.

Design / composition with siblings (#24, #26)

Chose the "second checkbox" / dedicated allowSpecialTags param approach (which the ticket lists as acceptable) rather than folding a 3-way select into nacc_special. This deliberately leaves nacc_special and its default-state handling untouched so it composes cleanly with #24 (the default-state fix) instead of reimplementing that logic — the new "allow" flag layers strictly on top.

• Add usage documentation to the NACC settings page #26 documents the Settings → NACC help copy. This PR adds one new control with its own label + one-liner ("Allow Visitors To Toggle Specialty Keytags") — flagging it here so Add usage documentation to the NACC settings page #26 can reflect it.
• Shared readme.txt / version bump: per the ticket comment, the version + changelog are shared across Specialty keytags show by default even when the setting is unchecked #24/Allow admins to disable specialty keytags entirely (hide the toggle) #25/Add usage documentation to the NACC settings page #26. I made the smallest correct entry and bumped to 6.0.2. Reviewer: please manage the combined bump — Specialty keytags show by default even when the setting is unchecked #24/Add usage documentation to the NACC settings page #26 should land under this same 6.0.2 rather than bumping again (avoid a double-bump).

Verification

• npm run build (vite) — bundle regenerated; npm run format:check + npm run lint clean.
• php -l clean; phpcs (.phpcs.xml) exit 0.
• Confirmed in the built bundle: allowSpecialTags = c !== false, checkbox creation gated behind this.allowSpecialTags, and the false branch forces showSpecialTags off.

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https://claude.ai/code/session_01KgsQa1xaRefJi29WCZzbQq