feat(ui): migrate tool live-output stream onto @maka/ui chat primitives (#332 PR3)

[Astro-Han]

Summary

Moves the tool live-output stream panel (ToolOutputStream) onto the @maka/ui chat substrate, retiring the bespoke .maka-tool-output-stream-* shell CSS with zero visual change. This is PR3 of the #332 conversation-flow governance pass, following PR1 (#334, bubble/row shell) and PR2 (#337, turn markers).

The panel's static shell (container, header, counts row + its pills, scrolling body, chunk/tag spans) literalizes onto a new internal streamVariants cva exactly as PR2 did for markers. The pulsing "live" dot is the one part that can't ride those rails — an animation can't be a leaf-literal and getComputedStyle reads a phase-dependent value — so it moves onto a new governed LiveIndicator primitive backed by a single canonical @keyframes maka-pulse, pinned by a keyframe-values contract instead of the diff harness.

Why

Closes part of #332 (PR3). The conversation-flow display is being migrated onto one @maka/ui substrate + a test net, one island at a time, with zero visual change. PR3 covers the tool live-output stream. It also lays the groundwork for retiring the repo's duplicated pulse keyframes: the duplicate reasoning / composer / onboarding live dots can adopt LiveIndicator in a follow-up motion pass, retiring their own *-pulse keyframes onto maka-pulse.

Scope

Changed:

• packages/ui/src/primitives/chat.tsx — add streamVariants (internal, off-barrel like markerVariants) for the panel shell, and an internal LiveIndicator primitive for the live dot. Every shell value is a LITERAL arbitrary utility that compiles 1:1 to the retired declaration.
• packages/ui/src/index.ts — LiveIndicator and streamVariants both stay OFF the package barrel (single consumer today, applied by relative import). LiveIndicator is promoted to a public export only when a second real consumer migrates onto it, not speculatively before then.
• packages/ui/src/components.tsx — wire ToolOutputStream to the primitives. Live auto-scroll behavior is preserved verbatim.
• apps/desktop/src/renderer/maka-tokens.css — add the canonical @keyframes maka-pulse (rest opacity 0.55, scale 1→1.1) in the shared motion home.
• apps/desktop/src/renderer/styles/tool-stream.css — delete the .maka-tool-output-stream-* block + its per-feature @keyframes.
• package.json — add npm run check:chat-visual, a discoverable entry point for the computed-style diff (the repo has no CI; this keeps the zero-visual proof reproducible by anyone).
• Tests + the computed-style diff script (see Verification).

Not included:

• Cross-feature pulse consolidation (reasoning-panel / composer / onboarding adopting LiveIndicator and deleting their duplicate keyframes) — a separate motion pass; that is where their visuals would change, so it stays out of this zero-visual PR. That pass is also when LiveIndicator would be promoted to a public export.
• The live auto-scroll behavior is untouched; MessageScroller / scroll-area governance remains the separately-evaluated feat(ui): govern chat conversation-flow display onto @maka/ui Base UI primitives #332 concern.
• Preview surfaces (terminal / diff / web-search) — PR4.

Verification

• npm run -w @maka/ui test — 12/12 (adds a streamVariants literal/scale-drift guard + the LiveIndicator pulse-pin test).
• npm run -w @maka/desktop test — 1604/1604 (adds chat-stream-cascade-contract.test.ts: retired stream selectors + per-feature pulse keyframe absent, canonical maka-pulse frames pinned, and the live-dot literals pinned — the one part the computed-style diff can't cover).
• npm run typecheck — clean across all workspaces.
• npm run check:chat-visual -- <pre-PR2 baseline.css> <head.css> (wraps scripts/check-chat-marker-computed-style.mjs, extended to cover the stream shell): against a pre-PR2 renderer CSS baseline (e033a8c4~1, which still carries both the bespoke marker and stream CSS), every row is 45/45 identical — TOTAL DIFFS: 0 across 36 element/state rows + 2 ::before middots (markers + all 14 stream rows incl. the data-live accent ring). Non-vacuous: the baseline and head bundles genuinely differ in source, yet the migrated chrome reads byte-identical computed style on both sides.
• Live dot: pinned by the @keyframes maka-pulse frame contract + the LiveIndicator literals (same values as the retired dot, so visually identical by construction); the animation escapes the computed-style proof by nature.

User-facing impact

None — zero visual change by design, locked by the contract + diff above.

Reviewer notes

• streamVariants and LiveIndicator are deliberately off the barrel (like markerVariants): one consumer today, applied by relative import, so they stay internal, freely-removable styling details rather than public API. When a second consumer (reasoning / composer / onboarding) actually migrates, LiveIndicator gets promoted to public then.
• The tests intentionally do NOT re-assert the stream shell's per-part class literals: that shell is proven by the computed-style diff, so re-stating the strings would only mirror the implementation. The source-string assertions are kept only for the live dot, which the diff cannot observe.
• The maka-pulse keyframe lives in maka-tokens.css because @maka/ui ships no CSS of its own (its primitives style via app-provided tokens); a keyframe is a named global rule, not a leaf utility, so this is the same kind of token dependency as --accent. Reduced-motion suppression rides on the primitive's motion-reduce: utilities.
• word-break:break-word stays an arbitrary literal, not Tailwind's break-words (which is the different overflow-wrap property).