refactor(emcn): share filled stop icon across chat controls

[BillLeoutsakosvl346]

Public chat, organization chat, and workspace chat each implemented the same filled stop icon inline. Add one StopFilled icon to EMCN and use it at all three call sites, preserving the original SVG geometry, caller classes, accessible button names, and stop handlers.

Follows #7975. That PR merged before this branch was prepared, so this branch starts at its merge commit and targets staging directly. The product changes are the shared icon, its barrel export, and the three consumer updates.

CI also exposed an existing race in the desktop terminal-selection test: its fixture read the buffer after a fixed 30 ms delay, before xterm necessarily finished parsing. Replace the delay with the completion callback of a trailing empty write. The fixture now waits for all preceding writes without changing its assertions or desktop runtime code.

Validation:

• Full external category audit: duplicate-artwork findings reduced from 3 to 0; no missing-button-name findings remain.
• Final committed-diff linter: zero introduced usage violations. Its two expected system-change notices identify the new central icon and barrel export; source equivalence was checked for both. The new icon's generic SVG props spread produces the same control-presence uncertainty as other reusable icons; all three consumers pass only their existing classes.
• Source equivalence check: expanding StopFilled recreates the original SVG and all non-import component syntax at all three call sites, including size, light/dark fill classes, conditions, and handlers.
• All 36 existing composer, user-input, and chat-streaming tests pass.
• All 1,657 desktop tests across 71 files pass after the CI test correction; desktop type checking and the changed test's Biome check pass.
• App and EMCN type checks, scoped Biome checks, API validation, and git diff --check pass.

The landing-page demo retains its copy under the existing landing exclusion. The external linter, verification scripts, reports, and dependency installation are not part of this PR.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Sep 18, 2026 7:28pm UTC

[cubic-dev-ai]

No issues found across 5 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no actionable regressions identified.

Summary

The PR centralizes the duplicated filled stop SVG as an EMCN icon while preserving the existing controls.

• Adds and exports the reusable StopFilled icon.
• Replaces three equivalent inline SVGs without changing button labels, handlers, conditions, dimensions, or colors.
• Consolidates the workspace send-button icon imports through the supported icons entry point.

_{Reviews (1) · Last reviewed commit: "refactor(emcn): share filled stop icon a..."}