Von Enhanced Transactions zu Parsed Events migrieren

Migrate this codebase from the Helius Enhanced Transactions API to the Helius
Parsed Events API.

## Background

Parsed Events is the successor to Enhanced Transactions. Same host
(https://mainnet.helius-rpc.com) and api-key query parameter; new paths,
JSON bodies, and response shapes.
Docs: https://www.helius.dev/docs/parsed-events/quickstart.md and
https://www.helius.dev/docs/parsed-events/parsed-response.md

## Step 1: Find the old call sites

Search for:
- POST requests to /v0/transactions
- GET requests to /v0/addresses/<address>/transactions (any query parameters)
- Pagination loops using before-signature / after-signature cursors, and
  handlers for the "Failed to find events within the search period" error

## Step 2: Rewrite each call site

Parse transactions:
- POST /v0/transactions -> POST /v1/parsed-events/transactions
- Body keeps { transactions: [...] }; optionally add commitment
  ("confirmed" default or "finalized") and includeRawTransaction.

Transaction history:
- GET /v0/addresses/{address}/transactions?... ->
  POST /v1/parsed-events/transaction-history with a JSON body.
- Parameter mapping (query -> body): address path segment -> address;
  limit -> limit (default is now 100, not 10);
  before-signature -> beforeSignature (prefer paginationToken, see below);
  after-signature -> afterSignature; sort-order -> sortOrder;
  commitment -> commitment (default is now "confirmed", not "finalized";
  "processed" unsupported);
  gt-time/gte-time/lt-time/lte-time -> time.gt/.gte/.lt/.lte;
  gt-slot/gte-slot/lt-slot/lte-slot -> slot.gt/.gte/.lt/.lte.
- type=... has no server-side equivalent: filter returned items client-side
  on parsed.summary?.type (lowercase: "swap", "transfer", ...) or on
  parsed.instructions[] (programId / instructionName).

Response shape changes:
- Each item is now { signature, parserStatus, parsed } — check
  parserStatus === "OK" and read fields from parsed.
- Field renames: timestamp -> parsed.blockTime; description ->
  parsed.summary?.description; type -> parsed.summary?.type;
  source -> parsed.summary?.parsedData?.protocol or
  parsed.instructions[].programName; events -> parsed.summary?.parsedData.
- nativeTransfers: unchanged shape under parsed.nativeTransfers.
- tokenTransfers: tokenAmount (pre-scaled decimal) is replaced by
  rawTokenAmount (raw integer string/number) plus decimals — divide by
  10**decimals where the old amount was used.
- History responses wrap results as { data, paginationToken }. Loop while
  paginationToken is present, passing it back in the next request body.
  Delete continuation-signature error handling for the old runtime type
  search — it no longer exists.

## Step 3: Constraints and cleanup

- Keep the same Helius API key and host; only paths, methods, bodies, and
  response handling change.
- Never hardcode an API key; keep reading it from the existing config or
  environment variable.
- Preserve the surrounding code style and error handling conventions.
- Leave Enhanced Transaction webhook payload handling unchanged — this
  migration covers only the /v0/transactions and /v0/addresses REST calls.

## Step 4: Verify

- Run the project's type checks and tests.
- Do NOT make any API calls yourself. Instead, write a standalone script
  (e.g. scripts/verify-parsed-events-migration.mjs) that fetches one page of
  history for an address from both APIs — the old
  GET /v0/addresses/{address}/transactions and the new
  POST /v1/parsed-events/transaction-history — and prints whether the
  signature sets, fees, and native transfer amounts match, listing any
  differences. Read the API key from an environment variable and the address
  from a CLI argument.
- Tell the user how to run it, for example:
  HELIUS_API_KEY=... node scripts/verify-parsed-events-migration.mjs <address>
- Summarize every call site changed and flag any you were unsure about.