feat: add app-config driven native tab visibility

[najuna-brian]

Description

Adds native tab visibility control from app.config.json for custom apps.

Custom apps can now decide which bottom tabs are shown using:

• navigation.tabs: ["Home", "Sync", "More"] (whitelist, ordered)
• navigation.tabs: [] (hide tab bar)
• no navigation key (default behavior: show all native tabs)

Supported visible tab IDs:
Home, Forms, Observations, Sync, More
Closes #350

---

What changed

• Added visible-tab constants/types (VISIBLE_MAIN_TABS, VisibleMainTab)
• Extended app config type with optional navigation.tabs
• Refactored MainTabNavigator to:
  • read navigation.tabs from AppConfigService
  • validate configured tab IDs at runtime
  • warn + skip invalid values
  • preserve configured order
  • render tabs dynamically
  • hide tab bar when tabs: []

Settings, About, and Help remain hidden tab routes (unchanged behavior).

---

How it works (flow)

custom app app.config.json
        │
        ▼
AppConfigService.loadConfig()
        │
        ▼
MainTabNavigator.getConfiguredTabs()
  - no navigation.tabs  -> default visible tabs
  - invalid tab values  -> warn + skip
  - []                  -> hide tab bar
        │
        ▼
Dynamic Tab.Screen rendering (in configured order)

---

Example for custom apps (app.config.json)

{
  "$schema": "https://ode.dev/schemas/app-config-v1.json",
  "name": "My Custom App",
  "version": "1.0.0",
  "navigation": {
    "tabs": ["Home", "Sync", "More"]
  },
  "theme": {
    "light": { "...": "..." },
    "dark": { "...": "..." }
  }
}

---

Behavior notes

• This is UI navigation control only.
• It does not restrict Formulus API access (openFormplayer, getObservations, etc.).

[r0ssing]

Looks great! I was wondering if a blacklist would have been better 🤔, but I think you're right to choose a whitelist! This will mean that if in the future wr add some new button to Formulus, people would have to update their custom apps to get it, instead of it popping up automatically.. I think this is a good design principle, so we ensure minimal 'surprises' for the users 🦒🤙

[najuna-brian]

Properly stated about the whitelist and it what I had in mind choosing it over blacklist