Viewer: pagination, search filtering, and per-sender hide with show-hidden toggle

[zbuc]

Problem

The viewer renders the entire sender table at once — 1,400+ rows on a realistic dataset — with no way to find a specific sender or dismiss ones you don't care about.

Proposal

Front-end only (web/, so the Pages demo inherits it via #19/#20):

• Search filter: text input, case-insensitive substring match on sender addresses
• Pagination: client-side, 50 rows per page, prev/next controls with page info
• Hide button: an emoji button on each row that hides that sender from the list and subtracts its count from the Total messages tile (top-sender and distinct-senders tiles recompute too); hidden senders persist in localStorage
• Show hidden toggle: reveals hidden senders (dimmed, with an unhide button) without adding them back into the totals

Acceptance criteria

• Works in both the local viewer and the static demo (no server changes needed)
• Sender strings still rendered exclusively via textContent (they are attacker-controlled)
• Search and pagination compose (filtering resets to page 1; page clamps when rows disappear)
• Hidden state survives reload; totals always exclude hidden senders
• build_demo.py anchors (Generate the Pages demo from web/ at deploy time #20) remain intact so the demo build keeps working