Warn on 1-byte path hash: channel 'Sent with' badge, packet detail and node badge (recommend 2/3-byte) #353

Channel messages show a "Sent with: N-byte" badge (renderSenderPathHashBadge() in public/channels.js, added in #212). The operator wants senders to use a 2- or 3-byte path hash. A 1-byte hash collides often across nodes, so it should read as a warning.

Proposal

• For size 1, render a warning variant of the badge. Sizes 2 and 3 stay unchanged and neutral.
  • Add a modifier class .ch-path-hash-badge--warn.
  • Colour the text with a new CSS variable --path-hash-warn, defaulting to var(--danger). That variable is already themed for light and dark. Map it in the customizer (THEME_CSS_MAP). No hardcoded colours.
  • Do not rely on colour alone. Add a small Phosphor warning icon (aria-hidden), plus text for screen readers.
  • Tooltip: explain the collision risk and recommend 2- or 3-byte. Take the name of the companion setting from the MeshCore firmware/docs (firmware/), not from guesswork.
• Hardcode the threshold ("1 = warning") for now. A customizer option for the recommended minimum can come later (AGENTS.md rule 8).

Also in scope (operator decision 2026-10-07)

Apply the same warning, with the same variable, icon and tooltip, wherever a 1-byte path hash is shown:

• Packet detail: the "HASH SIZE" row when it is 1 byte (public/packets.js).
• Node detail: today the "Multibyte" badge appears only for 2- and 3-byte (renderNodeBadges, public/nodes.js ~335). Add a small warning badge when the node advertises a 1-byte hash, with the same wording.

Reuse one shared helper for "is this size a warning" and the badge markup. Do not add one copy per page (DRY).

Acceptance

• Unit tests:
  • 1-byte gets the warn class, the icon and the tooltip;
  • 2- and 3-byte get no warn class;
  • invalid or missing sizes render no badge, as today.
  • Kill a mutant, e.g. a warn class on 2-byte.
• The same tests for the packet detail row and the node badge.
• Browser check of channels, packet detail and node detail in light and dark theme and on mobile. XSS gate clean.