PI fixes from live class testing

[sethbern]

Fixes several issues noticed during live peer instruction sessions:

• Clear per-student chat catch-up state on next question / vote 2 / next
  vote so the chat panel doesn't reappear empty on the next question
• Count messages from question start, not vote-2 start, so the message
  count doesn't reset to 0 mid-question
• Show a vote 1 prompt to students, matching the existing vote 2 message
• Show assignment title on the after-class student page
• Simplify non-LLM justification submit button text to "Submit"
• Default new peer questions to Generic LLM mode when an API key is
  configured, via async_mode column default (migration included)

Note on peer.css: while testing this I found that the chat panel rendered unstyled /staticAssets/css/peer.css (from the "restore and move peer.css" commit) because the file was never added to the nginx static assets.

[Copilot]

Pull request overview

Fixes multiple Peer Instruction (PI) UX/state issues discovered during live sessions, including chat catch-up state handling, message counting behavior across vote phases, and several student-facing text/UI tweaks. It also changes the default async_mode for new peer questions and adds a migration to apply the new DB default.

Changes:

• Clear assignment-scoped per-student Redis catch-up state on vote/next transitions; adjust client handling of enableChat catch-up and include assignment_id in relevant control messages.
• Count instructor dashboard “message count” from question start (not vote-2 start) by adding message_start_time.
• UI/text improvements: vote-1 prompt shown to students, assignment title displayed on after-class page, and simplified reflection submit text; default async_mode updated to llm with migration.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
migrations/versions/d8e4f2b6c1a7_default_async_mode_to_llm.py	Sets DB server default for assignment_questions.async_mode to 'llm' (and downgrades to 'standard').
components/rsptx/templates/staticAssets/js/peer.js	Adds/adjusts client catch-up handling and includes assignment_id in control messages.
components/rsptx/templates/assignment/student/peer_question.html	Adds an initial vote-1 prompt message for students.
components/rsptx/templates/assignment/student/peer_async.html	Displays assignment title on after-class page; simplifies non-LLM reflection submit button text.
components/rsptx/templates/assignment/instructor/peer_dashboard.html	Sends message_start_time and exposes assignment_id for downstream control messages.
components/rsptx/db/models.py	Changes ORM-level default async_mode to "llm".
bases/rsptx/assignment_server_api/routers/peer.py	Clears assignment-scoped Redis state on key phase transitions; counts messages from question start; filters async explainer messages.

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[sethbern]

This should be good whenever you get the chance to review @bnmnetp