feat(core): network fallback precedence, locale-safe formatting, lazy-import failures, clipboard recovery (#136–#139)

[Gbemi-programmer]

Closes #136
Closes #137
Closes #138
Closes #139

Note: the issues target dev, but the repo has no dev branch right now, so this is based on main.

#139 Network-configuration fallback precedence

• resolveNetwork(stored, env): persisted selection > NEXT_PUBLIC_STELLAR_NETWORK > testnet. Unknown values are ignored at every level. NetworkProvider uses it.
• resolveEndpoint(override, fallback): endpoint env overrides are used only when they are valid http(s) URLs with no embedded credentials. Otherwise the default is used.
• redactEndpoint(): shows only origin and path in diagnostics, so no query/fragment/userinfo secrets appear.
• Tests: precedence matrix, malformed URLs, credential-bearing URLs, redaction.

#138 Locale-safe date and amount formatting

• Documented fallback policy: a malformed locale tag falls back to the runtime default instead of throwing (safeLocales, used by both amount and date formatters).
• Tests: zero, negatives, 1-stroop precision, int64 bounds, Arabic/Devanagari digits, RTL (he-IL) negatives, invalid timestamps, UTC for any locale. No floating-point math on amounts.

#137 Registry lazy-import failure states

• loadFeaturePanel() returns a typed Result. A rejected import becomes load_failed with { slug, errorName } only (no message or stack, so no URLs or tokens leak into telemetry).
• /tools/[slug] still 404s for unknown slugs. An installed slice that fails to load now shows a recovery screen instead of a blank page or a 500. generateStaticParams is unchanged.
• Tests: resolved import, rejected chunk load, non-Error rejection, unknown slug. No network calls.

#136 Clipboard permission-denied recovery

• copyText throws a typed ClipboardError (unavailable | denied).
• tryCopyText never throws. It falls back to execCommand("copy") and returns "copied" only when a copy actually happened.
• CopyableValue shows an accessible role="alert" hint with the full value, selectable, when copying fails. It never claims success.
• Browser-mock tests: success, API unavailable, permission denied, fallback selection, and the component's success and failure UI.

Checks

• New and affected suites pass; lint is clean on the changed files; tsc shows no new errors.
• main already fails tsc and 21 vitest tests in 11 files. This branch has the identical set of failures and adds no new ones.
• registry.ts on main referenced generatedFeatures without importing it; the import is added here because [Core] Define registry lazy-import failure states #137 changes this file.

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