fix(ui-uitk): strip hidden U+FE0F and link orphaned reference files

[chris-addison]

What

Two related documentation-hygiene fixes in the UI skills. Grouped into one PR since both are validator findings from the same run and the diff is nine lines; CONTRIBUTING allows batching related skills when noted.

1. Hidden Unicode (the error)

The skills.sh Snyk W021 audit flagged SEC_HIDDEN_UNICODE in ui-uitk:

✗ ui-uitk
  ERROR [SEC_HIDDEN_UNICODE] references/custom-elements.md:20 — hidden/invisible character U+FE0F

A U+FE0F variation selector trailed the warning glyph in the heading on line 20. It is stripped; the visible U+26A0 glyph is kept, so the heading still renders as ### ⚠ CRITICAL: Namespace Declaration. That bare form is already how the rest of the repo writes the glyph (see levelplay-unity-integration/references/best-practices.md).

A scan of every .md/.json/.yaml/.txt file in the repo for variation selectors, BOM, zero-width, bidi-control and soft-hyphen characters confirms this was the only occurrence, and that the tree is now clean.

2. Orphaned reference files (the warnings)

The same run reported eight REF_ORPHAN warnings — seven in ui-uitk, one in ui-ugui.

The files were not actually undocumented: both SKILL.md files listed them, but as backticked paths rather than markdown links. The validator strips inline code before collecting link targets, so a backticked path never counts as a link and the reference reads as unreachable.

Converted the reference-list entries to markdown links. This matches ui-imgui, which already uses the linked form, and mirrors the same conversion made for levelplay-unity-integration in #38. Inline prose mentions elsewhere in the body are left as backticks, also matching ui-imgui.

No reference files were added, removed, or renamed.

Verification

node scripts/checks/validate-skills.mjs skills --profile hub

Before → after for the two affected skills:

Skill	Before	After
ui-uitk	1 error, 7 warnings	✓ clean
ui-ugui	0 errors, 1 warning	✓ clean

Note for reviewers

The same validator run reports a pre-existing HUB_LEAK error in unity-cli/SECURITY.md:21 on main. It is unrelated to this change and is already addressed on the in-flight unity-cli/safe-mode-recovery-and-install-accuracy branch, so it is deliberately untouched here.

[Copilot]

Pull request overview

This PR performs small documentation-hygiene fixes for Unity UI skills to satisfy repository validation: it removes a hidden Unicode variation selector (U+FE0F) and converts “orphaned” reference-path listings into real Markdown links so validators can detect them.

Changes:

• Convert ui-uitk reference list entries from backticked paths to Markdown links.
• Strip the hidden U+FE0F variation selector from a heading in ui-uitk reference docs while preserving the visible warning glyph.
• Convert the ui-ugui ScrollView reference entry into a Markdown link.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
skills/ui-uitk/SKILL.md	Converts reference entries to Markdown links so reference files are link-reachable by validators.
skills/ui-uitk/references/custom-elements.md	Removes hidden U+FE0F variation selector from a heading to resolve hidden-unicode validation errors.
skills/ui-ugui/SKILL.md	Converts the ScrollView reference entry to a Markdown link to prevent orphaned-reference warnings.

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