fix(desktop): cap emoji picker search-icon size in shadow root

[kchung]

What

Cap the emoji picker's search-icon size inside the <em-emoji-picker> shadow root so a runaway magnifying-glass ("loupe") can't balloon over the search field and emoji grid.

Why

emoji-mart renders the search bar's loupe and clear controls as inline SVGs and sizes them with a stylesheet it injects into its own shadow root. When that stylesheet hasn't applied by the time the SVG paints, the loupe falls back to its intrinsic size and renders as a giant icon covering the search input and the "Frequently used" row (see screenshot).

This is not a Buzz regression:

• The picker component was introduced once (feat(desktop): replace hardcoded emoji pickers with full emoji-mart picker #122) and the emoji-mart dependency (5.6.0) has never been bumped since — git log on EmojiPicker.tsx, desktop/package.json, and pnpm-lock.yaml shows only release-tag commits, no functional change to the picker.
• Nothing in Buzz's CSS targets the search loupe. The shadow CSS we inject for the avatar editor sizes the category-nav icons (#nav svg) but never the search loupe.
• The most likely trigger is the Tauri/WebKitGTK webview on Linux, where shadow-DOM style application can race first paint (same family as the issues in docs/linux-rendering-troubleshooting.md, though that doc doesn't cover this one).

How

Inject a tiny defensive stylesheet into every picker's shadow root that hard-caps the search-icon size. It:

• Reuses the existing shadow-DOM plumbing in disableSearchInputCorrections, which every call site already runs (composer, reactions, status), so all pickers are covered — not just the avatar editor.
• Is idempotent (#buzz-emoji-search-icon-fix id guard prevents re-injection).
• Only ever shrinks a runaway icon: the 1.3em values match emoji-mart's intended glyph size, so it's a no-op when emoji-mart's own CSS is present.

.search .icon,
.search .icon svg,
.search > svg { height: 1.3em; width: 1.3em; }

.icon covers the current markup; svg directly under .search guards against markup shifts across emoji-mart versions.

Testing

• biome check passes clean on the changed file (run via the repo's hermit biome).
• Full tsc --noEmit / biome check . / unit tests could not be run locally in this environment: corepack can't fetch pnpm (self-signed cert in the chain), so desktop/node_modules isn't installed. Relying on CI to run the full desktop lint/typecheck/test gate.
• Change is a small, JSX-free addition to an already-typed function using DOM APIs already used in this file.

Reviewer note: if you can repro the giant loupe on a Linux build, confirming it's gone with this branch would be the ideal manual check.

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🐝 Filed from a Buzz channel. Opened as a draft per standing preference.

[kchung]

Verification — dev server + before/after

Booted the desktop dev server (vite, ?e2e=mock) and drove the emoji picker with a headless browser.

Reproduced the reported bug and confirmed the fix constrains it:

State	Loupe SVG size
Bug (emoji-mart's icon sizing not applied, no defensive style)	288 × 288 px
With this PR's defensive style applied	20 × 20 px

Measured directly from the shadow root via getBoundingClientRect(). The 288px runaway matches the ~300px giant magnifier in the original report.

Left (red): the runaway loupe covering the search field + "Frequently used" row. Right (green): with this PR, the loupe is a small glyph tucked back inside the search box.

I also confirmed via the live shadow DOM that this PR's #buzz-emoji-search-icon-fix stylesheet is injected into the picker's shadow root and that its selectors match the real emoji-mart markup: <span class="icon loupe flex"><svg viewBox="0 0 20 20">…</svg></span>.

Full gate (run locally at HEAD)

• tsc --noEmit: clean
• biome check .: clean on the changed file (repo had 1 pre-existing unrelated warning)
• Unit tests: 4535 passed, 0 failed

Note: Chromium reliably applies emoji-mart's shadow stylesheet, so the giant loupe does not occur there under normal conditions — it's the Linux/WebKitGTK webview that races the paint. The before/after above reproduces the failure condition explicitly (emoji-mart icon sizing removed) to demonstrate the defensive cap works regardless.

[kchung]

Closing per Kevin Chung's request — another contributor is picking up this work. Diagnosis + fix left here for reference.