Add tracked and freeform tag editing

AGENTS.md

@@ -40,15 +40,17 @@ making changes; it is the authoritative operations and deployment runbook.
 
 ## Tags and filtering
 
-- Treat the child records under `content/tags/` as the single controlled tag
-  vocabulary. Their lowercase, hyphenated directory names are the canonical
-  slugs stored in entry `tags` fields and used in public tag URLs.
-- Keep the entry model's checkbox choices dynamically sourced from
-  `content/tags/`; do not duplicate the vocabulary in model configuration or
-  introduce free-form spelling and capitalization variants.
-- Add a tag record before assigning its slug to an entry. When renaming or
-  retiring a tag, update all references deliberately and verify that no orphan
-  slug or broken tag URL remains.
+- Treat the child records under `content/tags/` as the tracked tag registry.
+  Their lowercase, hyphenated directory names are the canonical slugs used in
+  public tag URLs. Entry `tags` fields may also contain normalized freeform
+  slugs without matching registry records.
+- Keep the entry model's tracked checkbox choices dynamically sourced from
+  `content/tags/`; do not duplicate the registry in model configuration.
+  Freeform entry tags remain visible but nonlinked and are excluded from
+  tracked-tag discovery.
+- Tracking or untracking a slug must not rewrite content references. Slug
+  renaming is separate: update all references deliberately and verify that no
+  old slug or broken tag URL remains.
 - Preserve normal links to dedicated tag pages as the no-JavaScript baseline.
   Client-side filtering must remain a progressive enhancement with semantic
   buttons, keyboard support, and an announced result count.
@@ -86,10 +88,10 @@ making changes; it is the authoritative operations and deployment runbook.
 - When template changes rely on updated CSS or other static assets, increment
   the relevant cache-busting version in the template and verify that generated
   pages reference the new asset URL.
-- For taxonomy changes, verify every entry tag has a matching `content/tags/`
-  record, tag counts match rendered project/devlog/blog/article usage,
-  dedicated tag URLs build, and listing filters work with valid, absent, and
-  unknown query values.
+- For taxonomy changes, verify tracked-tag counts match rendered
+  project/devlog/blog/article usage, freeform tags remain visible and unlinked,
+  dedicated tracked-tag URLs build, and listing filters work with valid,
+  absent, and unknown query values.
 - Run `git diff --check` and review the exact diff before committing.
 - If a push was requested, verify the Gitea Action result, deployed revision,
   and site health instead of treating a successful `git push` as completion.