feat(app): let the HUD follow the ticker's stand, act on the shown sender, and float it over other apps

[khagele]

Closes #555

The problem

The HUD was written from every capture, before the filter ran. Narrow the map to one target and the readout still jumped to every passer-by on the public channel. It was read-only: selecting or ignoring that sender meant opening the target sheet. And the moment another app came in front, there was nothing left to look at.

My changes in this PR

Two commits, one per half of the issue.

One filtered/all stand for the ticker and the HUD (state.rxMode). The ticker's header toggle reports through onModeChange and takes setMode back; the HUD's Filtered/All pill flips the same stand. With a filter set you look at the filtered set on both. In filtered mode the HUD keeps the last reception the filter let through, with that reception's own RSSI, SNR, sender and age. A closed eye on the pill says the filter kept something out since then; the count is in the aria-label and tooltip. Flipping to All puts the last capture on the HUD at once.

Quick actions on the shown sender: Target (only this one, the popup's Isolate), Add (to the selection) and Ignore, through the events the map popup and the target sheet already use. Target and Add follow the list's own rule, exported as isTargetKind. The pure rules are in app/src/hudmode.js.

The float readout (app/src/floatreadout.js). Float draws the HUD's reading onto a canvas, streams it into a <video> and takes that fullscreen. Chrome for Android moves a fullscreen video into its picture-in-picture window by itself when you press Home or switch apps; Chrome's Media Session auto-PiP is desktop-only, so fullscreen is the path. The window shows the tier colour as tint and bar, the RSSI, SNR and age, the sender, the stand with the eye, the BLE and MQTT dots, and Disconnected in amber. Android's previous/next buttons on the window (Media Session previoustrack / nexttrack) scrub the ticker's playhead, so the window steps through the same list the ticker shows. Where the browser lacks canvas capture or a way to take a video out of the page, the button is not shown.

FAB stack +34 px, the height of the new row, so the clearance above the HUD is unchanged. Decision log: docs/2026-09-04-hud-follows-the-filter.md. Changelog entries in both copies.

Verification

Suite	Result
app vitest	926 passed, build and eslint clean
web vitest	509 passed
web e2e whatsnew.spec.js, --fail-on-flaky-tests	13 passed (the changelog copies)

Seven mutation checks on the HUD tests, each red on one test. Browser at 360x780 and 412x915, feeding a signed advert through the capture path from the console: two receptions kept out by a target filter show the eye; All shows the last capture; the ticker's toggle flips the HUD's pill; Target sets the chip and reads active. The row uses 302 of 328 px at 360 with the float button, 320 with the eye. FAB clearance above the HUD is 60 px on both widths, as before. The float canvas draws as designed, stepping back moves the playhead to the previous reception with its own age, stepping forward to the newest makes it follow again, and closing pauses the stream and resets the button.

Not verified here, and worth a field check: whether Android Chrome floats a muted canvas-stream video the way it floats a playing clip, and whether the page keeps its timers while it does. The browser pane cannot go fullscreen without a real tap. The capture path is unchanged either way.

Decisions worth a look

• The stand is not persisted; the ticker's never was, and the app opens on filtered.
• Sound still cues every capture regardless of the stand (app: two thirds of what the radio hears is permanently silent, and the filter mutes the rest #468).
• updateHud still renders from the capture-time record; app: the HUD sender freezes at capture time, so a name that resolves later never reaches it #453 stays open.
• The float's fullscreenchange handling waits 600 ms before treating a fullscreen exit as a close, because Android hands a fullscreen video to its PiP window in two steps.

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