ci: tune the release-notes workflow - Opus 5, house style rules, completeness audit

[biswaroop1547]

Two changes to publish-release-notes.yml, both from what the v1.5.0 entry needed by hand after the workflow produced its first draft.

Model: claude-opus-4-8 → claude-opus-5.

House rules in the prompt. The generated draft was structurally fine and editorially thin: it duplicated Highlights in the body, clubbed unrelated capabilities into one line, wrote "a new default model" instead of naming Kimi K3 and positioning it, missed the iOS launch entirely, included a licensee-only integration nobody asked for, and used em dashes. The prompt now states the house style explicitly:

• hyphens not em dashes, straight quotes
• Highlights are scannable one-liners that do not repeat the body, one capability per line
• each section is a bold label plus one to four plain sentences
• lead the biggest capability by answering the objection a buyer actually has, then generalise
• concrete examples over abstractions, and say where a setting lives when it is user-changeable
• name the model and position it, never "a new default model"
• an app-store release gets its own section with the link inline
• omit licensee-only integrations unless asked
• drop anything with no user-visible symptom rather than inventing a benefit

Completeness audit. The draft also missed features whose commit subjects did not use conventional-commit prefixes. The prompt now requires building the full PR list from the source bodies, checking the entry against it item by item, excluding changes reverted inside the same window, and naming every deliberate omission in the closing summary.

No behaviour change to the git/PR mechanics.