feat(core): add error classification and default HTTP config (3/3)

[abueide]

Summary

• Adds classifyError() for SDD-compliant HTTP error classification
• Adds parseRetryAfter() supporting seconds and HTTP-date formats
• Adds ErrorClassification type to types.ts
• Adds defaultHttpConfig to constants.ts with SDD defaults
• Preserves maxPendingEvents (used by analytics.ts)

Merge order

Depends on #1152. Rebase onto master after #1152 lands.

1. feat(core): add UploadStateMachine for rate limiting (1/3) #1153 — UploadStateMachine + rate limit types
2. feat(core): add BackoffManager for transient error backoff (2/3) #1152 — BackoffManager + backoff types
3. feat(core): add error classification and default HTTP config (3/3) #1150 (this) — Error classification + defaultHttpConfig

Components

classifyError() (35 lines)

Classifies HTTP status codes per the SDD error handling tables.

Precedence: statusCodeOverrides -> 429 special handling -> default4xx/5xxBehavior -> permanent fallback

Returns: { isRetryable, errorType: 'rate_limit' | 'transient' | 'permanent' }

parseRetryAfter() (18 lines)

Parses Retry-After header values.

• Supports seconds format: "60" -> 60
• Supports HTTP-date format: "Fri, 31 Dec 2026 23:59:59 GMT" -> calculated delay
• Clamped to maxRetryInterval (default 300s)

defaultHttpConfig (27 lines)

Production-ready defaults per the SDD:

• Rate limiting: enabled, 100 retries, 300s max interval, 12h max duration
• Backoff: enabled, 100 retries, 0.5s base, 300s max, 12h max duration, 10% jitter
• Status code overrides: 408/410/429/460 retry, 501/505 drop

Test plan

• Existing test suites pass (no broken imports)
• maxPendingEvents still exported and importable
• No unrelated diffs

[abueide]

Note: Unit tests for error classification will be added in a separate PR to keep the review focused on the implementation.