feat: detect read-only functions and hide Submit for view calls

[OTimileyin]

Closes #17
Title: feat: detect read-only functions and hide Submit for view calls

Summary

• extractFunctions in contract-parser.ts now emits isReadOnly: null for every function at parse time — the Soroban XDR spec (ScSpecFunctionV0) exposes no readonly/view attribute, so the spec path is unavailable and null is the correct initial state.
• simulateCall in invocation.ts now returns { value, isReadimulation it readsresult.transactionData.getFootprint().readWrite().length === 0` — an empty write set means no ledger mutations → read-only.
• useContract exposes a new patchFunctionReadOnly(name, isReadOnly) callback that immutably updates the matching function in metadata state.
• ContractExplorer calls patchFunctionReadOnly after every seadOnly` is lazily resolved per-function on first use.
• FunctionForm hides the Submit button entirely when fn.isReadOnly === true. Simulate remains the primary action and is always visible.
• FunctionList renders a view badge next to the function signature when fn.isReadOnly === true.

How read-only is determined

Soroban simulation returns a SorobanDataBuilder (transactionDvery ledger key the function reads or writes. If readWrite()` is empty the function made no state changes and is treated as read-only. This check runs client-side after the simulation RPC call — no extra network round-trip.

Unknown-status fallback

Before any simulation has run, isReadOnly is null. The UI tralse` — both Simulate and Submit are shown. This guarantees noregression: functions that have never been simulated behave exactly as before.

Test cases (6 passing)

Suite	Case	Assert
function-form	isReadOnly: null	Simulate ✓ Submit ✓
function-form	isReadOnly: true	Simulate ✓ Submit absent
function-form	isReadOnly: false	Simulate ✓ Submit ✓
function-list	isReadOnly: true	"view" badge present
function-list	isReadOnly: false	no badge
function-list	isReadOnly: null	no badge

Test Suites: 2 passed, 2 total
Tests: 6 passed, 6 total

Security note

Read-only detection is informational only — it removes a confusi gate actual transaction submission at the protocol level. A user who somehow bypasses the UI can still call invokeCall directly; Soroban's own fee and auth checks remain the authoritative guard.

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[RaymondAbiola]

@OTimileyin please resolve existing conflicts