fix(desktop): render text reaction fallbacks safely

[AaronGoldsmith]

Summary

• Render no-URL literal kind-7 reactions as bounded text unless the content is exactly one well-formed native emoji grapheme.
• Strip only valid outer shortcode colons for presentation (for example, :missing_reaction: displays as missing_reaction), while preserving raw reaction content for titles, accessibility, and toggle identity.
• Apply the same bounded fallback presentation in hover popovers so unresolved shortcodes and long arbitrary text cannot overflow the fixed glyph area; the separate reaction name remains raw.
• Keep image custom emoji exclusively driven by the NIP-30 emojiUrl branch.
• Bound and left-align long literal reaction text so it truncates without overlapping its count.

Kind-7 reaction content is literal under NIP-25, so existing or legacy arbitrary-text events retain their meaning and are rendered safely rather than rejected. NIP-30's matching emoji tag / resolved emojiUrl remains the only custom-image signal.

This is intentionally different from:

• fix(relay): stop panic when reacting to a project root or comment #4973, which fixes a relay ingest panic for reactions on channel-less project events.
• fix(desktop): integer-align custom reaction emoji #4779, which fixed custom-image alignment, not no-URL literal fallback rendering.

This PR is Desktop-only: it changes no relay ingest, persistence, protocol, or channel derivation. A possible CLI warning for an unknown :shortcode: sent without --emoji-url is intentionally deferred and not coupled to rendering compatibility.

Reproduction

buzz reactions add --event <event-id> --emoji :missing_reaction:

The resulting kind-7 event has no matching NIP-30 emoji tag, so Desktop must treat the content as a text fallback rather than forcing it into a native-emoji box.

Testing

• pnpm biome check src/features/messages/ui/MessageReactions.tsx src/features/messages/lib/reactionGlyphPresentation.ts src/features/messages/lib/reactionGlyphPresentation.test.mjs src/shared/lib/emojiOnly.ts tests/e2e/reaction-names.spec.ts
• pnpm test (4,373 passed)
• pnpm build:e2e
• pnpm exec playwright test tests/e2e/reaction-names.spec.ts (3 passed), covering:
  • NIP-30 custom-image hover regression
  • unresolved shortcode pill + hover popover
  • arbitrary ship it pill + hover popover
  • long literal pill/count geometry, truncation, and hover overflow bounds
• sq agents review main...HEAD --local ... after addressing its malformed-ZWJ finding (final local review: no findings)

Screenshots from Testing

Pill row: unresolved shortcode, arbitrary text, and long literal text — each bounded, left-aligned, and truncated without overlapping its count

Case	Rendering
Short unresolved shortcode in hover popover — outer colons preserved in the raw reaction name
Max-length literal content in hover popover — wraps within the popover instead of overflowing the glyph area

Original UI rendering bug example