fix(ts-sdk): export version constant

[realfishsam]

Summary

• Export a TypeScript __version__ constant from the package root to match the Python SDK public module version surface.
• Keep the value aligned with the Python SDK's current pmxt.__version__ value.

Fixes #1568

Test Plan

• git diff --check
• node + TypeScript transpileModule syntax check for sdks/typescript/index.ts
• Attempted targeted tsc compile; blocked by missing committed generated client artifacts (sdks/typescript/generated/src/index.js), so no generated stubs were committed.

[realfishsam]

PR Review: FAIL

What This Does

Adds a TypeScript package-root __version__ export so consumers can inspect the SDK version from pmxtjs.

Blast Radius

TypeScript SDK package root sdks/typescript/index.ts; no sidecar/core behavior changes.

Consumer Verification

Before (base branch):
sdks/typescript/index.ts did not export __version__.

After (PR branch):
The PR exports __version__, but the value is hardcoded to "2.17.1" while sdks/typescript/package.json at the PR head is 2.18.0 (node/git show check in this run). A consumer importing __version__ from the package root would receive stale version metadata.

Test Results

• Build: PASS for current main core build during scheduled run
• Unit tests: PASS for current main core Jest (699 passed, 3 skipped)
• Server starts: N/A for package-root metadata
• E2E smoke: FAIL by package metadata check (__version__ value does not match package.json)

Findings

1. sdks/typescript/index.ts:29 — export const __version__ = "2.17.1"; is stale relative to sdks/typescript/package.json version 2.18.0. This would immediately publish incorrect SDK version metadata and will drift again on every release unless generated/read from package metadata.

PMXT Pipeline Check

• Field propagation (3-layer): N/A
• OpenAPI sync: N/A
• Financial precision: N/A
• Type safety: OK
• Auth safety: N/A

Semver Impact

patch -- package metadata export fix, but current value is wrong.

Risk

Published npm consumers would see the wrong __version__, undermining diagnostics and support workflows.