Companion: rules-based, context-aware writing advice

Replace the kitten's random generic tips with a deterministic, LLM-free
prose checker that reads the actual document and surfaces one gentle,
bilingual note at a time — quoting a slice of her own sentence so the
advice is clearly about *this* draft.

Rules (all conservative, tuned for a Mandarin-native ESL writer):
run-ons, comma splices, unclear antecedents, Oxford comma, a/an,
uncountable plurals, capitalize languages/days/months, subject-verb
agreement, plural-after-number, double determiner, "there is" + plural,
its/it's, than/then, comma-after-transition, doubled words, lowercase
"i", sentence capitals, and spacing around punctuation.

Each rule is paired with false-positive guards (e.g. "a university",
"After dinner, I went home and read", existing Oxford lists) and pinned
by a 45-case Vitest suite (npm test).

Also: bubbles now linger proportional to how much there is to read
(zh+en) and pause-on-hover, so denser advice no longer vanishes mid-read.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

web/src/components/Companion/PetalCompanion.tsx

@@ -9,6 +9,7 @@ interface Props {
   saveStatus: SaveStatus
   editTick: number
   acceptTick: number
+  text: string
 }
 
 // Emoji placeholder per mood, used for any mood a companion has no Lottie for.
@@ -26,8 +27,14 @@ const STORAGE_KEY = 'petal.companion'
 // useCompanion and shows a Mandarin-first speech bubble for cheers, tips, and
 // break reminders. Clicking the mascot opens a picker to switch companions
 // (the choice persists in localStorage).
-export function PetalCompanion({ wordCount, saveStatus, editTick, acceptTick }: Props) {
-  const { mood, bubble, dismiss } = useCompanion({ wordCount, saveStatus, editTick, acceptTick })
+export function PetalCompanion({ wordCount, saveStatus, editTick, acceptTick, text }: Props) {
+  const { mood, bubble, dismiss, holdBubble, releaseBubble } = useCompanion({
+    wordCount,
+    saveStatus,
+    editTick,
+    acceptTick,
+    text,
+  })
 
   const [companionId, setCompanionId] = useState<string>(() => {
     try {
@@ -136,6 +143,8 @@ export function PetalCompanion({ wordCount, saveStatus, editTick, acceptTick }:
         <div
           role="status"
           onClick={dismiss}
+          onMouseEnter={holdBubble}
+          onMouseLeave={releaseBubble}
           className="petal-bubble pointer-events-auto max-w-[260px] cursor-pointer p-3 pr-3.5"
           style={{
             background: 'var(--color-surface)',