Fix clipped "Allow Wallet" permission dialog.

[djscruggs]

Problem

The first party "Allow Wallet" permission popup opened at a fixed height of
230px, plus a 30px URL bar allowance applied only when the user agent looked
like Firefox. The wallet row was cut off mid-line:

• The URL bar sniff was wrong. Chrome and Safari also show a URL bar in
  popups, and no user agent string predicts the real chrome height — the
  browser subtracts its own chrome from the height passed to window.open by
  an amount that varies with browser, platform, and user settings.
• 230px was too small for real content. A site with a web app manifest
  renders a 48px icon above a name line and an origin line. The no-manifest
  case (a small default glyph and a bare origin) fits; the real one does not.

The dialog is laid out to exactly fill the popup with one internally scrolling
region, so content that did not fit was clipped rather than made
scrollable. This is why the symptom is a half-visible wallet row with the
Block/Allow footer still in view — the document never overflows and the footer
is pinned outside the scroll region, so neither a document-level scroll check
nor a footer-position check detects it.

Fix

1. Apply the chrome allowance on every browser, and raise the base height
   260 (DEFAULT_ALLOW_WALLET_POPUP_HEIGHT = 290).
2. Have the popup measure its own content once loaded and resize to fit,
   replacing both guesses with a measurement. Over-allowing height now costs
   nothing, since a popup with more viewport than it needs shrinks.

The sizing decision is a pure function, getWindowHeightAdjustment, clamped to
the available screen height, a 160px minimum usable height, and a 400px maximum
single adjustment. fitWindowToContent is the DOM shell around it: it measures
the scrolling region (not just the document, which never overflows here) and is
a no-op wherever resizing is not permitted, so a popup that cannot resize still
works — it just scrolls.

Resizing runs after nextTick() and after images settle, because an icon that
has not loaded yet contributes no height.

Verification

Measured against a real cross-origin CHAPI wallet driving the actual popup,
bodyOverflow = pixels of greeting clipped inside the scrolling body:

	viewport	clipped
main	193px	40px
this branch	253px	0

In a real window.open popup, fitWindowToContent grows a 200px popup by
33px, a 230px popup by 3px, and leaves a 290px popup unchanged — overflow 0 in
all three.

Tests: 11 unit tests for the sizing logic (npm run test:unit, Node's
built-in runner — no new dependency) and 12 geometric-invariant e2e tests for
the dialog, passing on Chromium, Firefox, and WebKit. Confirmed red before the
fix.

Note that Playwright pins the viewport, so resizeBy is inert under it by
design: the e2e tests assert the CSS/content invariant at a given height, and
the resize arithmetic is covered by the unit tests.

Notes for review

• urlBarHeight is shared with DEFAULT_HINT_CHOOSER_POPUP_HEIGHT and
  DEFAULT_CROSS_DEVICE_HINT_CHOOSER_POPUP_HEIGHT, so making it unconditional
  also gives those popups 30px more room on Chrome and Safari. That is the same
  correction, and safe now that oversized popups shrink to fit — but it is a
  wider blast radius than the allow-wallet dialog alone and worth a look.
• The test harness had a blind spot. /test/wallet-chooser passed
  manifest: null, so it never rendered the icon and name that cause this bug.
  This PR adds manifest support (name=, manifest=0). The existing gallery
  screenshots were taken under that blind spot.
• CI runs lint only (.github/workflows/main.yml, Node 24) and does not
  run either test suite, so the new tests do not gate this PR. Lint passes. I
  ran unit + e2e locally.
• Pre-existing failure, not from this branch: wallet-chooser.spec.js →
  "has no horizontal overflow" fails 5× on stock main as well (verified by
  stashing). It is the documented KNOWN FAILING test awaiting the
  vue-web-request-mediator extraction.
• Per DB release convention this changes the CHANGELOG only (7.6.1, day
  left as dd); package.json's version is untouched. The one
  package.json change is adding the test:unit script.

[djscruggs]

Screenshots showing new message and how modal expands to handle long message.