Give Extopy a visual direction of its own

[nathanfallet]

Extopy was Material 3 with a red swapped in: stock components, one type style for everything, and
a palette that was iOS system greys on a Material scheme. This gives it a direction of its own.

#D9534F is fixed by the project and stays exactly as it is. What changed is how much room it
gets: it tints every neutral in the app, and only saturates on the current tab and a liked heart.

The theme

Three files, the way nutrimaxing-app has it.

Color.kt builds both schemes around the red — no grey in here is neutral, which is what stops a
mostly-monochrome feed from looking like a system dialog. Type.kt gives the author's name, the
handle, the body and the timestamp four distinct styles; they all shared the default body style
before, which is why a post read as one flat block of text. Theme.kt assembles those with a
softer shape scale, and carries the two colours Material has no role for — a liked heart and a
repost are states of a post, not "primary" or "error".

liked is deliberately not the brand red. It used to be exactly primaryColor, so a liked
heart was indistinguishable from the accent. repostedColor was #008000, a pure green belonging
to no palette; it is now desaturated to sit beside the red.

Components of our own

Three stock components are replaced rather than themed, because theming them was not enough:

• NavigationBar → a pill floating clear of the screen edge, current tab filled rather than
  carrying a small indicator behind its glyph. It respects the navigation-bar inset, which the old
  one did not — it sat under the gesture bar.
• OutlinedTextField → a filled pill on BasicTextField. The stock field brings a container,
  a floating label slot, an indicator line and a 56 dp minimum height, all of which fight a
  rounded shape. Used by search and by the composer.
• The post counters → bubbles grouped on the left, instead of icons spread across the whole
  card by SpaceEvenly, which made them read as a detached toolbar rather than as metadata of the
  text above them.

The fourteen hand-maintained icon XMLs are gone, replaced by Phosphor, which brings outline and
filled weights for everything. Only three of the old ones came in pairs, and one was not referenced
at all.

Tabs are no longer destinations

The four tabs were navigation destinations, so switching between them ran a navigation transition
across the whole screen — for a move that goes nowhere. They are now state inside MainScreen,
held in a rememberSaveable.

That also settles where the tab bar belongs: inside MainScreen. A post, a profile or the composer
are opened on top of a tab, so they simply do not have one — there is no visibility rule to get
wrong.

Which makes a back affordance mandatory rather than nice to have: those three screens had a
CenterAlignedTopAppBar with no navigation icon at all, so without the bar there was no way back
on Android, which has no edge swipe. ExtopyTopBar gives them one.

The bar also stopped guessing which tab is current. It used to compare
route.lowercase().startsWith(item.name.replace("_", "")) — a string comparison between an enum
name and a route class name, which renaming a screen would have broken in silence.

Bugs found on the way

Not design, but they were in the screens being touched:

• "Follow" and "Following" had their styles the wrong way round: the filled button was on the
  already following state, so following someone made the button louder rather than quieter.
• AccountView printed the display name twice — the second line was meant to be the handle.
• A missing biography, and a repost with no body, each left an empty line that looked like a
  rendering fault.
• Settings headed an Accounts section that had nothing in it.
• Direct messages and notifications rendered nothing at all. They now say they are coming — an
  empty screen reads as a failure, not as an unfinished feature. So does an empty timeline, which
  used to be a black screen.

Localisation

Following LOCALIZATION.md in nutrimaxing-docs turned up two real gaps:

• CFBundleLocalizations was missing from the Info.plist, so iOS treated the app as
  English-only: no Language entry in Settings, and one language on the App Store listing, for six
  translations actually shipped. knownRegions was already right, which is what made it easy to
  miss.
• No locales_config.xml and no android:localeConfig, so the per-app language picker Android
  13+ offers never appeared.

Also two escaped apostrophes in the French strings: Compose does not unescape \', so
"Nom d'utilisateur" rendered with the backslash visible.

New strings are translated in en, fr, de and es; bs, hr and sr fall back to English until someone
who speaks them writes the sentences. The three profile figures had their labels derived from the
existing translations rather than retranslated.

Verified

Android debug and release, the 17 tests, both iOS frameworks, and the app running on the simulator
against a local backend — in both light and dark, which is where the two grounds were tuned.

Not verified: navigation by hand. Tapping the simulator needs an accessibility permission the
terminal does not have, so switching tabs, opening a post and coming back are checked by reading
the code, not by using it. Worth thirty seconds of your thumb before merging. Android runtime is
still unverified too — the local AVDs have no system image installed.

Still open, and untouched here

TimelineViewModel._users is never populated, so the UserCard this PR restyles never actually
appears in the timeline. And LogoutUseCase still has no entry point in Settings. Both predate
this branch.

Note that merging runs the deploy jobs again; they currently fail on their own (missing Ruby on the
runner, and the fastlane match SSH key), so nothing ships either way.