fix(core): centralize time defaults

[realfishsam]

Summary

• Add shared core time utilities for timestamp unit detection and WebSocket reconnect defaults
• Standardize timestamp seconds/milliseconds heuristics across core and SDK server managers
• Standardize exchange WebSocket reconnect fallbacks on a shared 5s default and preserve explicit 0 values with nullish coalescing

Fixes #206
Fixes #225

Test Plan

• git diff --check
• python3 -m py_compile sdks/python/pmxt/server_manager.py
• npm run build --workspace=pmxt-core (attempted; tsc was killed by the local environment with exit 137)
• npx tsc --noEmit --pretty false --incremental false --skipLibCheck (attempted; killed by the local environment with exit 137)

[realfishsam]

PR Review: FAIL

What This Does

Centralizes reconnect/timestamp defaults across exchange WebSockets, normalizers, and SDK server-manager status conversion. This should be an internal cleanup with no intended SDK response-shape change.

Blast Radius

Core WebSocket clients for Gemini Titan, Kalshi, Limitless, Opinion, Probable; Polymarket/Probable normalizers; Python and TypeScript server-manager status helpers.

Consumer Verification

Before (base branch):
Base branch has duplicated literals such as 5000ms reconnect delays and local timestamp seconds/ms conversion. I could not run a consumer API comparison because the PR branch does not build.

After (PR branch):
PR branch fails before the sidecar can start: npm run build --workspace=pmxt-core reports src/exchanges/probable/websocket.ts(2,33): error TS2440: Import declaration conflicts with local declaration of 'QueuedPromise'.

Test Results

• Build: FAIL (npm run build --workspace=pmxt-core TypeScript error)
• Unit tests: NOT RUN (build failed)
• Server starts: FAIL (server not started because build failed)
• E2E smoke: FAIL (blocked by build failure)

Findings

1. core/src/exchanges/probable/websocket.ts:2 imports QueuedPromise from ../../types while the same file still declares local interface QueuedPromise<T> at line 7. TypeScript rejects the duplicate name, so the core package cannot build and the sidecar cannot ship.

PMXT Pipeline Check

• Field propagation (3-layer): N/A
• OpenAPI sync: N/A
• Financial precision: N/A
• Type safety: ISSUE — duplicate QueuedPromise declaration prevents compilation
• Auth safety: N/A

Semver Impact

patch -- intended internal cleanup, but currently unmergeable because it breaks the build.

Risk

No runtime behavior could be verified because the TypeScript build fails.